Fahrenheit to Celsius Converter: US Weather, Cooking Temperatures, and Fever Guide
Convert Fahrenheit to Celsius instantly using the exact formula: °C = (°F − 32) × 5/9. Includes cooking oven temperatures, fever thresholds (98.6°F = 37°C), US weather reference, batch conversion for recipes, Kelvin output, and free PDF export.
Fahrenheit to Celsius Calculator
Enter a temperature to convert
Accepts any value including negatives. 32°F = 0°C. 212°F = 100°C. −40°F = −40°C (crossover).
Temperature Scale Reference (°F vs Key Benchmarks)
Why the United States Uses Fahrenheit When Most of the World Uses Celsius
The United States is the only major industrialized country that uses the Fahrenheit scale for everyday temperature measurement in weather, cooking, and medicine. Germany, the UK (mostly), and the rest of the world transitioned to Celsius decades ago, but the US kept Fahrenheit because the changeover cost was never seen as worth the disruption. The Fahrenheit scale was proposed by German physicist Daniel Gabriel Fahrenheit in 1724. He set 0°F at the freezing point of a saltwater brine solution, 32°F at the freezing point of pure water, and 96°F at what he believed was average human body temperature (later revised to 98.6°F = 37°C exactly). The resulting scale put the typical human comfort range between 0°F and 100°F, which Fahrenheit saw as elegant.
The Celsius scale, proposed by Swedish astronomer Anders Celsius in 1742, takes a simpler scientific approach: 0°C at the freezing point of water and 100°C at its boiling point at standard atmospheric pressure (1 atm, sea level). Most scientists, engineers, and medical professionals worldwide use Celsius or Kelvin. In the US, scientific and medical settings often use Celsius internally (body temperature charts in hospitals, laboratory protocols, NIST standards), while consumer-facing contexts like weather forecasts, oven dials, outdoor thermometers, and home thermostats remain in Fahrenheit.
The Exact Conversion Formula and Why It Works
The conversion from Fahrenheit to Celsius is: °C = (°F − 32) × 5/9. The subtraction of 32 adjusts for the offset between the two scales (water freezes at 32°F vs 0°C). The multiplication by 5/9 adjusts for the different step sizes: one degree Fahrenheit is a smaller temperature change than one degree Celsius. Specifically, 180 Fahrenheit degrees span the same range as 100 Celsius degrees (from freezing to boiling), so the ratio is 100/180 = 5/9. The reverse formula (°F = °C × 9/5 + 32) uses 9/5 (the reciprocal) and adds 32 back. Note that 5/9 is a repeating decimal (0.5555…), so this calculator uses Big.js arbitrary-precision arithmetic to compute results at full mathematical precision rather than stopping at a rounded approximation.
One remarkable fact about these two scales: there is exactly one temperature where both read the same number. Solve °F = °C: x = (x − 32) × 5/9, so 9x = 5x − 160, giving 4x = −160, so x = −40. Both scales read −40 at the same temperature. This is not a coincidence you can derive without algebra: it is an exact mathematical consequence of the two formulas, and it is a useful sanity check for any conversion tool or mental math estimation.
How This Fahrenheit to Celsius Converter Works
Enter any temperature in Fahrenheit (or Celsius using the direction toggle) and the tool instantly returns the converted value, plus Kelvin (K = °C + 273.15) and Rankine (°R = °F + 459.67, used in US engineering thermodynamics). The context panel identifies what that temperature means in practical US terms: whether it is in the freezing range, comfortable indoor zone, fever territory, cooking range, or extreme heat zone. The batch mode accepts up to 20 temperatures at once, returning a table with all four scales (°F, °C, K, °R) plus a brief context note for each. This is particularly useful for bakers converting recipe oven temperatures from European cookbooks, meteorologists bridging US and international data sets, or nurses converting patient temperature readings between scales.
US Cooking and Oven Temperatures in Fahrenheit and Celsius
American recipes and US kitchen appliances use Fahrenheit exclusively. When cooking from a British, Australian, French, or European cookbook, you will almost certainly need to convert oven temperatures from Celsius to Fahrenheit. Here is the standard US oven temperature guide, with British Gas Mark equivalents used in many UK cookbooks.
| Description | °F | °C | Gas Mark | Best For |
|---|---|---|---|---|
| Very low oven | 250°F | 121°C | Gas 1/2 | Meringues, slow-drying, warming |
| Low oven | 300°F | 149°C | Gas 2 | Cheesecakes, slow-cooked braises |
| Moderately low | 325°F | 163°C | Gas 3 | Moist cakes, custards, pastry |
| Moderate (standard bake) | 350°F | 177°C | Gas 4 | Cakes, cookies, meatloaf |
| Moderately hot | 375°F | 191°C | Gas 5 | Pies, tarts, roasted vegetables |
| Hot oven | 400°F | 204°C | Gas 6 | Pizza, roast chicken, bread |
| Very hot | 425°F | 218°C | Gas 7 | Crispy potatoes, puff pastry |
| Extremely hot | 450°F | 232°C | Gas 8 | Neapolitan pizza, searing |
| Broil / Grill | 500°F+ | 260°C+ | Gas 9+ | Broiling, finishing, caramelizing |
Convection ovens (fan-forced in UK/Australian terminology) run hotter than conventional ovens because the fan circulates hot air, eliminating cool spots and accelerating cooking. The standard US rule is to reduce the oven temperature by 25°F (about 14°C) when using convection mode, or reduce cooking time by 25% while keeping the same temperature. So a conventional recipe calling for 350°F would become 325°F in a convection oven, or the cook time drops from 40 minutes to 30 minutes at 350°F. European recipes that specify “fan oven” temperatures have already accounted for the convection effect; do not reduce further when following those specs on a convection setting.
Deep Frying and Candy Temperatures in Fahrenheit
Two American cooking techniques require particularly precise temperature control in Fahrenheit: deep frying and candy making. For deep frying, oil temperature between 325°F (163°C) and 375°F (191°C) produces crispy, not greasy results. Below 325°F the food absorbs too much oil; above 375°F the exterior browns before the inside cooks. For candy making, the exact sugar temperature determines the texture of the final product: soft ball stage is 235°F to 240°F (113°C to 116°C) for fudge and fondant; firm ball stage is 245°F to 250°F (118°C to 121°C) for caramel; hard crack stage is 300°F to 310°F (149°C to 154°C) for hard candy and lollipops. These stages are defined by what happens when the hot sugar syrup is dripped into cold water, a test developed long before thermometers were common in kitchens.
Three Real US Temperature Conversion Examples
A French Visitor Checking Phoenix Weather in July
A family from Lyon, France visits Phoenix, Arizona in July. The AccuWeather forecast shows a high of 115°F. They are accustomed to French temperatures in Celsius and need to understand what 115°F means for their outdoor plans. Applying the formula: (115 − 32) × 5/9 = 83 × 5/9 = 415/9 = 46.1°C. For context, the highest temperature ever recorded in France was 45.9°C (114.6°F) in Gallargues-le-Montueux in June 2019, a national emergency. Phoenix regularly exceeds this in July, which is considered a normal summer day there. The visitors should plan all outdoor activities before 9 a.m. or after 7 p.m., wear breathable light-colored clothing, drink at least 1 liter of water per hour outdoors, and never leave children or pets in a parked car, where interior temperatures can reach 140°F (60°C) within minutes.
Converting a British Baking Recipe for a US Kitchen
An American home baker is following a Victoria sponge recipe from a popular BBC cookbook. The recipe instructs: “Bake at 180°C (fan) for 25 minutes.” She needs to convert this to her US oven’s Fahrenheit setting and decide whether to use her oven’s convection mode or regular bake. Converting 180°C: °F = 180 × 9/5 + 32 = 324 + 32 = 356°F. The “(fan)” notation means the recipe temperature already accounts for convection. So she has two options: set her convection oven to 356°F (or round to 350°F, close enough), or set her conventional oven to 356 + 25 = 381°F (round to 375°F) to compensate for the lack of forced air. She chooses 350°F convection and checks for doneness at 22 minutes since her convection oven runs slightly hot.
Pediatric Fever Assessment at a US Doctor’s Office
A parent brings a 4-year-old to a pediatrician in Austin, Texas. The triage nurse takes an ear (tympanic) temperature reading of 101.3°F and asks the parent to note the time and context. The parent, originally from Germany, is used to Celsius readings and wants to understand what 101.3°F means in metric terms. Converting: (101.3 − 32) × 5/9 = 69.3 × 5/9 = 346.5/9 = 38.5°C. According to the CDC and the American Academy of Pediatrics, a fever is defined as a rectal temperature at or above 100.4°F (38°C), or oral/tympanic at or above 100°F. At 101.3°F (38.5°C), this child has a confirmed moderate fever. The pediatrician may recommend acetaminophen (Tylenol) weight-dosed at 10-15 mg/kg every 4-6 hours if the child appears uncomfortable, staying well-hydrated, and monitoring for temperature rising above 104°F (40°C), which would warrant more urgent evaluation.
Four Expert Tips for Quick Fahrenheit and Celsius Conversions
The “Double and Add 30” Rule: Fast °C to °F Estimate
When you need a quick mental estimate of a Celsius temperature in Fahrenheit, double the Celsius value and add 30. This gives answers within 2 to 4 degrees of the exact value for the typical weather and cooking range. Examples: 20°C: double = 40, add 30 = 70°F (exact: 68°F). 25°C: double = 50, add 30 = 80°F (exact: 77°F). 35°C: double = 70, add 30 = 100°F (exact: 95°F). The mental shortcut works better for the 0°C to 40°C weather range than for cooking temperatures (180°C: rule gives 390°F, exact is 356°F, a bigger error). For cooking, use the exact conversion or the oven table above.
Memorize Five Key Benchmarks and Interpolate the Rest
You do not need to memorize the formula if you lock in these five exact anchors: −40 (same on both scales), 32°F = 0°C (freezing), 68°F = 20°C (room temp), 98.6°F = 37°C (body), 212°F = 100°C (boiling). Between those anchors, each 1°C equals 1.8°F. So 30°C is 20°C + 10°C = 68°F + 18°F = 86°F. 40°C is 68°F + 36°F = 104°F. This five-anchor interpolation method is fast, reasonably accurate for most purposes, and more reliable than the “double and add 30” approximation because it is anchored to known exact values rather than a rounded rule.
Wind Chill and Heat Index: Why Perceived Temperature Differs from Actual
The Fahrenheit temperature you hear in a US weather forecast is the actual air temperature. But what your body feels depends on wind speed (in cold weather) and humidity (in hot weather). The National Weather Service wind chill formula calculates perceived temperature in °F as: 35.74 + 0.6215T − 35.75V^0.16 + 0.4275T × V^0.16, where T = °F air temperature and V = wind speed in mph. At 20°F air temperature with 20 mph winds, the wind chill is about −2°F (−19°C), creating frostbite risk in 30 minutes on exposed skin. The heat index works in reverse: at 95°F (35°C) with 90% relative humidity, the heat index is about 131°F (55°C), the temperature a human body perceives. This is why Phoenix at 115°F with 5% humidity can feel more tolerable than Houston at 95°F with 90% humidity, despite the lower actual temperature.
Kelvin and Rankine: The Absolute Temperature Scales Used in US Engineering
For scientific and engineering calculations, especially in thermodynamics, the absolute scales matter because negative temperatures do not exist: absolute zero is the lowest possible temperature (0 K = −273.15°C = −459.67°F). Scientists worldwide use Kelvin: K = °C + 273.15. US engineers, particularly in aerospace and chemical engineering, often use Rankine (°R = °F + 459.67) because it is the absolute scale that pairs naturally with Fahrenheit-based engineering formulas. When you see a US thermodynamic textbook (like those used in ChE or aerospace programs) expressing the ideal gas law as PV = nRT, the R in that equation assumes T in Rankine when using US customary units. NASA’s shuttle-era aerodynamic heating calculations were performed in Rankine. This converter outputs both Kelvin and Rankine alongside the standard Fahrenheit-Celsius result.
US Weather Temperature Guide: Fahrenheit Reference for International Visitors
International visitors to the United States often find themselves trying to interpret Fahrenheit weather forecasts without a converter handy. Here is a practical guide to what common US weather temperatures feel like, with Celsius equivalents and appropriate clothing recommendations.
- Below 0°F (−17.8°C): Extreme cold. Wind chill warnings common. Frostbite risk on exposed skin in under 30 minutes. Layers essential; exposed skin should be covered. Common in Minnesota, Wisconsin, North Dakota in January.
- 0°F to 20°F (−17.8°C to −6.7°C): Very cold. Heavy winter coat, insulated boots, gloves, hat required. Black ice risk on roads. Snow likely in many northern US regions.
- 20°F to 32°F (−6.7°C to 0°C): Cold. Freezing temperatures. Snow or freezing rain possible. Roads may be icy. Coat, gloves, and hat required.
- 32°F to 50°F (0°C to 10°C): Cool to cold. Above freezing but you will notice the chill. Medium-weight coat suitable. Spring weather in much of the northern US.
- 50°F to 68°F (10°C to 20°C): Mild. Light jacket or sweater comfortable. Typical spring and fall weather across much of the US. San Francisco average all year.
- 68°F to 80°F (20°C to 26.7°C): Warm and comfortable. T-shirt and light clothes. The ideal outdoor temperature for most Americans. Typical of US spring and early fall across the South, mid-Atlantic, and Pacific coast.
- 80°F to 95°F (26.7°C to 35°C): Hot. Sunscreen needed. Humidity amplifies the felt temperature significantly in Florida, the Gulf Coast, and the Southeast.
- 95°F to 105°F (35°C to 40.6°C): Very hot. Heat advisory territory in many US regions. Limit outdoor exertion. High heat index likely in humid climates.
- Above 105°F (above 40.6°C): Extreme heat. Heat emergency in most of the US. Life-threatening for vulnerable populations. Common in Phoenix, Las Vegas, and the Sonoran Desert in summer.
Fahrenheit Temperatures Across US Industry, Medicine, and Food Safety Standards
The Fahrenheit scale is deeply embedded not just in everyday American weather and cooking, but in a wide range of US regulatory standards, food safety protocols, and industrial specifications that affect millions of people every day. Understanding these temperature benchmarks and their Celsius equivalents helps professionals across healthcare, food service, HVAC, and industrial operations communicate accurately when bridging US and international standards.
US Food Safety Temperature Standards in Fahrenheit
The USDA Food Safety and Inspection Service (FSIS) and the FDA Food Code set all US food safety temperatures in Fahrenheit. The “danger zone” for bacterial growth is 40°F to 140°F (4.4°C to 60°C). In this range, pathogens like Salmonella, E. coli O157:H7, and Staphylococcus aureus can double in number every 20 minutes. Key US food safety temperature requirements include: refrigerator storage at or below 40°F (4.4°C); ground beef cooked to a minimum internal temperature of 160°F (71.1°C); poultry cooked to 165°F (73.9°C); whole-muscle beef (steaks, roasts) cooked to 145°F (62.8°C) followed by a 3-minute rest; seafood cooked to 145°F (62.8°C); reheated leftovers to 165°F (73.9°C). Restaurant health inspections in all 50 states use Fahrenheit for these critical control points, while the international HACCP (Hazard Analysis and Critical Control Points) food safety framework used globally uses Celsius for the same benchmarks.
HVAC and Indoor Comfort Temperatures in the US
American heating, ventilation, and air conditioning (HVAC) systems and residential thermostats operate in Fahrenheit. ASHRAE Standard 55, published by the American Society of Heating, Refrigerating and Air-Conditioning Engineers, defines the US indoor thermal comfort zone as approximately 68°F to 76°F (20°C to 24.4°C) in winter and 73°F to 79°F (22.8°C to 26.1°C) in summer, depending on clothing level and activity. The standard US commercial building thermostat set point is typically 70°F (21.1°C) year-round. Energy Star and DOE recommendations suggest setting residential thermostats to 68°F (20°C) when occupied and 60°F (15.6°C) when unoccupied in winter to reduce heating costs by approximately 10% per 8-hour setback. In summer, Energy Star recommends 78°F (25.6°C) when occupied and 85°F (29.4°C) when unoccupied. Each Fahrenheit degree of thermostat adjustment represents a 1% to 3% change in heating or cooling energy use, making precise Fahrenheit-to-Celsius conversion relevant for energy auditors comparing US and international building energy benchmarks.
Industrial and Manufacturing Temperature Standards
American industrial facilities use a mix of Fahrenheit and Celsius depending on industry and the origin of the technical standard. Petroleum refining temperatures are specified in Fahrenheit in US API (American Petroleum Institute) standards: crude oil distillation separates into fractions from light gases at under 100°F (37.8°C) to heavy fuel oil at above 700°F (371.1°C). Steel heat treatment (annealing, normalizing, hardening) is specified in Fahrenheit in ASTM standards: low-carbon steel normalizes at 1,600°F to 1,700°F (871°C to 927°C); tool steel hardens at 1,400°F to 1,500°F (760°C to 816°C). Pharmaceutical manufacturing in the US FDA GMP framework specifies most process temperatures in Celsius (following ICH guidelines that use metric), creating a need for precise conversion when US operators trained in Fahrenheit work with internationally standardized batch records.
Altitude and Atmospheric Pressure Effects on Boiling Point
Across the United States, elevation differences create real variation in the boiling point of water that home cooks and food safety professionals must account for in Fahrenheit. At sea level (0 ft elevation), water boils at 212°F (100°C). At Denver, Colorado (5,280 ft), water boils at approximately 202°F (94.4°C). At the summit of Pikes Peak (14,115 ft), water boils at only about 184°F (84.4°C). These lower boiling temperatures mean pasta, eggs, potatoes, and other boiled foods require longer cooking times at altitude. The FDA Food Code adjusts required cooking temperatures for altitude: at elevations above 6,400 feet, commercially prepared foods must be cooked to internal temperatures approximately 10°F higher than sea-level standards to achieve the same pathogen kill, a correction that requires converting between the two scales for kitchen staff trained in either system.
Quick Reference: Fahrenheit to Celsius Conversion Table
| Fahrenheit (°F) | Celsius (°C) | Kelvin (K) | US Context |
|---|---|---|---|
| −40°F | −40°C | 233.15 | Crossover point (both scales equal) |
| 0°F | −17.78°C | 255.37 | Extreme US winter (Minnesota / Alaska) |
| 32°F | 0°C | 273.15 | Water freezes at sea level (exact) |
| 50°F | 10°C | 283.15 | Cool spring morning |
| 68°F | 20°C | 293.15 | Comfortable indoor (low end) |
| 72°F | 22.22°C | 295.37 | US thermostat / ASHRAE comfort |
| 77°F | 25°C | 298.15 | Warm room / lab standard temp |
| 98.6°F | 37.0°C | 310.15 | Normal adult body temperature (exact) |
| 100.4°F | 38.0°C | 311.15 | Clinical fever threshold (CDC) (exact) |
| 104°F | 40°C | 313.15 | High fever / Phoenix summer peak |
| 212°F | 100°C | 373.15 | Water boils at sea level (exact) |
| 350°F | 176.67°C | 449.82 | Standard US baking temperature |
| 451°F | 232.78°C | 505.93 | Fahrenheit 451: paper ignition temp |
Frequently Asked Questions About Fahrenheit and Celsius
The exact formula is: °C = (°F − 32) × 5/9. First subtract 32 to remove the scale offset (water freezes at 32°F but 0°C). Then multiply by 5/9 to account for the different step sizes (180 Fahrenheit degrees = 100 Celsius degrees). Examples: 98.6°F: (98.6 − 32) × 5/9 = 66.6 × 5/9 = 37.0°C exactly. 212°F: (212 − 32) × 5/9 = 180 × 5/9 = 100°C exactly. 32°F: (32 − 32) × 5/9 = 0°C exactly.
100°F = (100 − 32) × 5/9 = 68 × 5/9 = 340/9 = 37.7778°C (repeating 7). In practical medical context, 100°F (37.78°C) is slightly above the normal body temperature of 98.6°F (37°C) and a borderline low-grade fever. The CDC clinically defines fever as 100.4°F (38°C) for adults, so 100°F is technically below the formal fever threshold but often considered a sign to monitor for rising temperature. Note that 100°C (the boiling point of water) equals 212°F, a completely different temperature.
Normal adult body temperature is 98.6°F = 37.0°C exactly. This is the average; the healthy range is approximately 97°F to 99°F (36.1°C to 37.2°C). Body temperature varies by measurement site (rectal is typically 0.5°F higher than oral; tympanic/ear readings vary by technique), time of day (lowest in the morning, highest in late afternoon), and individual physiology. The CDC and American Academy of Pediatrics define fever as a rectal temperature at or above 100.4°F (38°C). Research published in journals including eLife has suggested the average body temperature in Western populations may have declined slightly over the past century to approximately 97.9°F (36.6°C), though 37°C remains the standard clinical reference.
37°C = 37 × 9/5 + 32 = 66.6 + 32 = 98.6°F exactly. This is the standard normal human body temperature. When a European doctor records a patient’s temperature as 37.0°C, the American equivalent on a US thermometer would be 98.6°F. At 38°C (100.4°F), clinical fever is confirmed. At 39°C (102.2°F), moderate fever. At 40°C (104°F), high fever requiring medical attention. At 41°C (105.8°F), dangerously high fever. At 42°C (107.6°F), life-threatening hyperthermia.
The two scales are equal at exactly −40 degrees: −40°F = −40°C. This is the only temperature where both scales show the same number. You can verify with either formula: (−40 − 32) × 5/9 = −72 × 5/9 = −360/9 = −40°C. Or: −40 × 9/5 + 32 = −72 + 32 = −40°F. In practical terms, −40° is an extreme cold temperature that occurs regularly in parts of Alaska, northern Canada, Siberia, and Antarctica. At this temperature, exposed skin freezes in minutes and most automotive fluids require special cold-weather formulations.
350°F = (350 − 32) × 5/9 = 318 × 5/9 = 1590/9 = 176.666…°C (176°C rounded, or 177°C). This is the most common baking temperature in American recipes, used for cakes, cookies, quick breads, meatloaf, and many casseroles. European recipes often specify 180°C for the same purpose, which converts to 356°F (close enough to use 350°F). If converting a European “fan oven” temperature, 180°C fan = approximately 180°C conventional + 25% more airflow, which in Fahrenheit would be set at around 350-360°F on a US convection oven.
The exact formula is: °F = °C × 9/5 + 32. Multiply the Celsius temperature by 9/5 (= 1.8), then add 32. Examples: 0°C: 0 × 1.8 + 32 = 32°F (water freezes). 100°C: 100 × 1.8 + 32 = 212°F (water boils). 20°C: 20 × 1.8 + 32 = 36 + 32 = 68°F. 37°C: 37 × 1.8 + 32 = 66.6 + 32 = 98.6°F. Mental math shortcut: double the Celsius and add 30 for a rough estimate (accurate within 3-5°F in the normal weather range).
The US adopted Fahrenheit early in its history, and the system became deeply embedded in infrastructure, education, consumer appliances, and cultural expectations before the global shift to Celsius. The Metric Conversion Act of 1975 encouraged metric use but did not mandate it for consumers, so everyday Americans continued using Fahrenheit for weather and Celsius never replaced it. The UK made a similar partial transition: UK weather forecasts switched to Celsius officially in 1975, but Americans continued without switching. In contrast, Australia, Canada, and most of Europe converted their weather forecasts and household thermometers to Celsius in the 1970s as part of broader metrication programs. The US also uses miles, pounds, and gallons for the same historical entrenchment reasons, making it one of three countries (with Myanmar and Liberia) that has not completed the metric transition.
Water boils at 212°F = 100°C at standard atmospheric pressure (1 atm = 101.325 kPa = 14.696 psi) at sea level. This is the exact definition of the top end of the Celsius scale. At higher altitudes, the boiling point decreases because atmospheric pressure is lower: at 5,000 feet (1,524 meters) elevation like Denver, Colorado, water boils at approximately 202°F (94.4°C). At 10,000 feet (3,048 m), water boils at about 194°F (90°C). This matters for cooking: pasta and potatoes take longer at altitude because water is boiling at a lower temperature. Pressure cookers (which operate above 1 atm) raise the boiling point to 250°F (121°C) or higher, cooking food faster than any open pot at any elevation.
The CDC and American Academy of Pediatrics define fever as: rectal temperature at or above 100.4°F (38°C) in any age group, or oral/axillary/tympanic temperature at or above 100°F (37.8°C). Practical guidelines by temperature: 100.4°F to 102°F (38°C to 38.9°C): low-grade fever, monitor and hydrate. 102°F to 104°F (38.9°C to 40°C): moderate fever, consider antipyretics, call doctor if in infants under 6 months or if other symptoms are present. Above 104°F (40°C): high fever, contact your doctor or urgent care. Above 105°F (40.6°C): call emergency services. For infants under 3 months: any temperature above 100.4°F rectally warrants immediate medical evaluation. Always consult a licensed medical professional for diagnosis and treatment decisions.
The coldest temperature ever recorded in the contiguous United States (the lower 48 states) was −70°F (−56.7°C) at Rogers Pass, Montana on January 20, 1954. Including Alaska, the US all-time record low is −80°F (−62.2°C) at Prospect Creek, Alaska on January 23, 1971. The world record low is −128.6°F (−89.2°C) at Vostok Station, Antarctica on July 21, 1983. For comparison, the freezing point of carbon dioxide (dry ice) is −109.3°F (−78.5°C), colder than any temperature naturally occurring anywhere in the US. Liquid nitrogen boils at −320.4°F (−195.8°C), and absolute zero is −459.67°F (−273.15°C), the lowest temperature theoretically possible.
Kelvin (K) is the SI absolute temperature scale used in science worldwide. Its zero point is absolute zero (−273.15°C = −459.67°F), the coldest theoretically possible temperature where all thermal motion stops. Kelvin degrees are the same size as Celsius degrees, just shifted: K = °C + 273.15. Key values: absolute zero = 0 K. Water freezes = 273.15 K. Water boils = 373.15 K. Normal body temperature = 310.15 K. Surface of the Sun = approximately 5,778 K. Note that Kelvin uses no degree symbol (you write “300 K” not “300°K”). The closely related Rankine scale (°R = °F + 459.67) is the absolute scale in the Fahrenheit system, used in US engineering thermodynamics where calculations require absolute temperature but engineers prefer to keep working in Fahrenheit units.
The heat index, sometimes called the “feels like” temperature, combines air temperature and relative humidity to estimate how hot the air feels to the human body. The National Weather Service heat index formula accounts for the fact that sweat evaporates more slowly in humid air, reducing the body’s cooling efficiency. Example: at 90°F (32.2°C) air temperature with 80% relative humidity, the heat index is 113°F (45°C). At the same 90°F with 30% humidity, the heat index is about 90°F (same as air temperature). The NWS issues heat advisories when the heat index exceeds 105°F (40.6°C) for at least 2 hours, and heat warnings when it exceeds 108°F (42.2°C). Heat index values above 130°F (54.4°C) represent extreme danger with heat stroke likely on exposure.
Tympanic (ear) and temporal artery (forehead) thermometers are convenient but less precise than rectal or oral thermometers. Studies show ear thermometers have variability of plus or minus 0.5°F to 1°F (0.3°C to 0.6°C) depending on technique, ear canal wax, and positioning. Forehead (temporal) scanners vary plus or minus 0.5°F to 1.5°F (0.3°C to 0.8°C). Rectal temperature is considered the gold standard and most accurately reflects core body temperature, running about 0.5°F (0.3°C) higher than oral readings. For clinical decision-making in a medical office, rectal or oral readings are preferred over tympanic for precise fever assessment. For home screening and general monitoring, ear and forehead thermometers are practical and acceptably accurate when used consistently with the same device and same measurement site.
The hottest temperature ever recorded in the United States (and the world, at the time) was 134°F (56.7°C) at Furnace Creek, Death Valley, California on July 10, 1913. While some scientists have questioned this reading’s accuracy due to instrument placement, it remains the official record. More recently, Death Valley recorded 130°F (54.4°C) on July 9, 2021, which is considered more reliably measured and may represent the highest reliable temperature reading in recorded history. Phoenix, Arizona routinely reaches 115°F to 120°F (46.1°C to 48.9°C) during summer heat domes. The western US has seen its all-time temperature records broken repeatedly in recent years due to intensified heat domes linked to climate change, with the Pacific Northwest reaching 116°F (46.7°C) in Portland, Oregon and 121°F (49.4°C) in Lytton, British Columbia in June 2021.
Yes. This tool is completely free with no account required, no ads, and all calculations run in your browser using Big.js arbitrary-precision arithmetic. The formulas °C = (°F − 32) × 5/9 and °F = °C × 9/5 + 32 are mathematically exact. Since 5/9 is a non-terminating repeating decimal (0.5555…), Big.js computes the result to full precision without the floating-point rounding errors that can affect a simple JavaScript calculation (for example, JS might give 98.6°F = 37.00000000000001°C; this tool gives exactly 37°C). The batch mode processes up to 20 temperatures simultaneously with all four scale outputs (°F, °C, K, °R), and the PDF export generates a formatted report with the full US temperature reference table.
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This Fahrenheit to Celsius converter is provided for educational and general informational purposes only. The conversion formulas °C = (°F − 32) × 5/9 and °F = °C × 9/5 + 32 are mathematically exact and consistent with definitions in NIST SP 811 and the International System of Units (SI). Kelvin conversion uses K = °C + 273.15 per BIPM definitions. All temperature outputs in this tool are calculated at full Big.js precision. Medical temperature information (fever thresholds, normal body temperature ranges, clinical guidelines) is based on publicly available CDC, American Academy of Pediatrics, and general medical reference information as of 2024, and is provided for informational context only. It is not medical advice. Always consult a licensed healthcare professional for diagnosis and treatment of medical conditions including fever. Oven temperature conversions are provided as general guidance; actual appliance calibration varies. Weather context (heat index, wind chill, regional records) is based on NOAA and National Weather Service reference data. Content written and reviewed by the USCalculators.com editorial team. References: NIST SP 811; BIPM; NOAA; CDC; AAP; ASHRAE Standard 55.