Free Math Calculators and Unit Converters: 110 Tools, No Signup
Convert any measurement, calculate percentages, split bills, track business days, and solve everyday math problems. Every tool is built for US units, works on any device, and gives instant results.
What Makes a Reliable Unit Converter?
A unit converter is a mathematical tool that transforms a measurement expressed in one unit into its exact equivalent in another unit by applying a precise, internationally defined conversion factor. For instance, one inch equals exactly 2.54 centimeters by definition set by the International Bureau of Weights and Measures. Multiply any inch value by 2.54 and you always get the correct centimeter result, without rounding error.
The United States operates on a dual measurement system. Day-to-day American life runs on US customary units including inches, feet, yards, miles, pounds, ounces, gallons, quarts, and Fahrenheit. Science, medicine, engineering, and international trade use the metric system: centimeters, kilograms, liters, and Celsius. Americans navigate between both systems constantly, whether reading a German appliance manual, filling a prescription measured in milligrams, or comparing tire sizes between domestic and imported vehicles.
A trustworthy converter uses the exact internationally ratified conversion factor, not a rounded approximation. It also explains what the numbers mean in real terms, because raw digits without context are only half the answer.
The Dual Measurement Reality in American Life
Most Americans learn imperial units at home and metric units in school science classes, which means both systems show up in everyday tasks. A carpenter in Houston measures lumber in feet and inches but reads European hardware specs in millimeters. A home cook in Chicago follows a recipe in cups and tablespoons but buys bulk ingredients labeled in grams. A trucking dispatcher in Atlanta weighs loads in short tons but fills out customs paperwork in metric tons for a Canadian shipment crossing the border.
The 110 tools in this hub cover every conversion that comes up in those daily situations. They are organized into 11 categories below, from cooking volume and distance to temperature and air pressure.
US Imperial Volume and Cooking Converters
These 11 tools handle the exact measurements printed on US recipe cards, measuring cups, and food labels. All conversions follow USDA and FDA definitions for US customary volume. Useful for home cooks, bakers, caterers, and anyone scaling a recipe or reading a foreign cookbook in metric.
US Imperial Length Converters
Six tools for converting within the US customary length system, from inches to feet to yards to miles. Used daily by contractors, real estate agents, landscapers, and anyone reading property surveys or construction blueprints in standard US dimensions.
Percentage Calculators: Discounts, Tax, Margin, and More
Eight everyday math tools that handle money calculations Americans run into constantly: figuring out a sale price, splitting a restaurant bill, calculating the markup on a wholesale item, or checking whether a salary offer is a real raise. These are the tools people reach for before pulling out a spreadsheet.
Time, Date, and Payroll Calculators
Nine tools covering the scheduling and payroll math that comes up in every US workplace, from tracking a contract deadline to converting hours and minutes into decimal time for a timesheet. The business days calculator includes all 11 US federal holidays recognized by the Office of Personnel Management.
Length Converters: Imperial to Metric and Specialty Units
Twenty-two length conversion tools covering every combination Americans actually need, from the everyday (inches to centimeters) to the specialized (furlongs to miles for horse racing, nautical miles for boating, light-years for astronomy). Every conversion uses the exact NIST-defined factor.
How Americans Convert Weight Between Pounds, Kilograms, and Tons
Fifteen weight conversion tools spanning everything from milligrams for medication doses to short tons for trucking and freight. The US uses pounds and ounces for everyday weight, but medicine uses milligrams, international grocery labels use grams, and shipping often requires kilograms or metric tons for customs declarations.
Volume Converters: Gallons, Liters, and Cubic Measurements
Sixteen volume tools handling the full range of US and metric liquid and dry volume units, plus cubic measurements for tanks, pools, and shipping containers. The US gallon (3.785 liters) differs from the UK imperial gallon (4.546 liters), so all tools on this page use the US definition.
Area Conversion Tools for Real Estate, Building, and Land Measurement
Ten area converters spanning the units US property owners, builders, and farmers actually encounter: square feet on floor plans, acres on deeds, square miles in county maps, and hectares in international agricultural data. The US Census Bureau publishes land area in both square miles and square kilometers, so both are covered here.
Temperature Converters
Three tools covering every temperature scale Americans use. Fahrenheit appears in daily weather, cooking, and home heating in the US. Celsius appears in science, medicine, and every other country in the world. Kelvin is used in chemistry, physics, and astrophysics where absolute temperature matters.
| Common Temperature | Fahrenheit (US) | Celsius | Kelvin |
|---|---|---|---|
| Absolute zero | -459.67 F | -273.15 C | 0 K |
| Water freezes | 32 F | 0 C | 273.15 K |
| Normal body temp | 98.6 F | 37 C | 310.15 K |
| Water boils (sea level) | 212 F | 100 C | 373.15 K |
| Oven at 350 degrees | 350 F | 176.7 C | 449.8 K |
Speed and Pressure Unit Converters
Seven tools for speed and pressure conversions used in transportation, aviation, weather, and automotive maintenance. The US uses MPH for road speed and PSI for tire pressure. Aviation uses knots. Science and weather reporting use metric. This set covers every combination.
Time Unit Converters
Three tools for simple time unit math: converting hours to minutes, weeks to days, and clock time to decimal hours. These come up constantly in payroll, project management, and scheduling, where software often requires decimal hours while people think in hours and minutes.
How to Get the Most Accurate Results From These Tools
Every tool on this hub uses internationally ratified conversion factors, not approximations. Here is how to use them for the best results in practical situations.
Pick the right category
Use the quick-jump menu at the top of this page to land directly on the tool type you need. Weight tools are separate from volume tools, because a pound of water and a pint of water are completely different measurements even though people mix them up constantly.
Enter the exact number from your source
Do not round before converting. If your tape measure shows 5 feet 7 and 3/8 inches, enter that exact fraction into the Feet and Inches to CM converter. Rounding first compounds the error through the conversion factor.
Check which gallon or ton you are working with
The US gallon (3.785 L) and the UK imperial gallon (4.546 L) are different. The US short ton (2,000 lbs) and the metric ton (2,204.6 lbs) are different. All tools here use US definitions unless the name says otherwise.
Use the companion tool for double-checking
Each category includes both directions of the conversion. After converting inches to centimeters, use the CM to Inches tool to confirm you get your original number back. A result that does not reverse cleanly signals a data entry error, not a math error.
Related Calculator Hubs That Use Math Every Day
Unit conversion and percentage math are foundations for dozens of specialized fields. These hubs apply the same math principles to specific American industries and activities.
Frequently Asked Questions About Unit Conversion and Everyday Math
110 Free Math Tools, All in One Place
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Browse All 110 ToolsLegal Disclaimer and Editorial Transparency
All conversion factors used on this page are sourced from official US and international standards bodies including the National Institute of Standards and Technology (NIST), the International Bureau of Weights and Measures (BIPM), and the US Office of Personnel Management for business day calculations.
Tools on this site are provided for informational and educational purposes. For professional applications in engineering, medicine, legal, or financial contexts, verify results against the applicable regulatory standard or consult a qualified professional. USCalculators.com does not warrant that results are suitable for any specific professional purpose.
Conversion factors are based on exact internationally ratified definitions where available (e.g., 1 inch = 2.54 cm exactly). For derived or compound conversions, intermediate rounding may introduce minimal variation at extreme decimal places. All tools are reviewed periodically for accuracy against current NIST publications.