Boat Fuel Range Calculator: GPH, Nautical Range, Multi-Leg Trip Planner, and Marine Fuel Cost Estimator
Built and reviewed by David (MBA Finance) · Updated October 2026
Three marine planning tools in one: calculate fuel range and GPH from engine HP with a throttle optimization table showing NMPG at five speed settings and sea condition corrections; plan multi-leg trips with per-leg fuel burn and a GO/NO-GO decision for each waypoint; or estimate exact trip costs with a fuel price sensitivity table. The US Coast Guard one-third rule is applied automatically. Detailed PDF report included.
⛵ Select Mode
🛥 Engine and Vessel
HP
Per engine. Tool multiplies by engine count. Common: Mercury 150 HP, Yamaha 250 HP, twin 300 HP = 600 HP total.
knots
gal
Total capacity. Typical: center console 50-150 gal, offshore sportfish 300-600 gal, trawler 500-1,500 gal.
gal
If blank, assumes 95% of tank capacity (5% unusable reserve).
🎯 Optional: Destination Check and Cost
nm
One-way distance. Gets a GO/NO-GO for the round trip based on the one-third rule.
$/gal
Marine fuel typically $0.50-$1.50 above pump prices. Check current marina prices.
⛵ Vessel Setup
gal
HP
$/gal
🗺 Trip Legs (up to 4)
🔵 Leg 1
🟡 Leg 2
🟢 Leg 3 (optional)
⚪ Leg 4 (optional return)
⛵ Fuel Consumption (enter one)
GPH
Most accurate. From digital fuel flow gauge at your typical cruise RPM. Per engine (tool multiplies by count).
HP
Leave GPH blank to estimate from HP. Per engine HP.
🗺 Trip Details
nm
One-way distance. Calculator shows both one-way and round trip costs.
knots
$/gal
gal
📊 Results
⛵
Calculate safe cruising range with one-third rule applied and a throttle optimization table showing NMPG at five speed settings. Or plan a multi-leg trip with per-leg fuel check and GO/NO-GO decision. Or estimate exact fuel cost for any trip with a price sensitivity table. Full PDF with throttle optimization and fuel cost analysis.
NMPG and Safe Range vs Speed
How Marine Fuel Range Works: GPH, NMPG, and the One-Third Rule Every Boater Must Know
Calculating how far your boat can travel on a tank of fuel requires three numbers: your fuel consumption rate in gallons per hour (GPH), your cruising speed in knots, and the amount of usable fuel aboard. The math is simple: divide your speed by your GPH to get nautical miles per gallon (NMPG), then multiply by usable fuel. What makes marine fuel planning genuinely different from driving a car is the one-third rule, the single most important guideline in recreational boating safety.
The one-third rule states: use the first third of your fuel to travel to your destination, the second third to return, and hold the final third as an emergency reserve. This means your safe planning range is only two-thirds of your theoretical maximum range. It is not a conservative suggestion, it is a practical requirement. In open water, you cannot stop and call a tow truck. If you encounter a headwind on the return trip, your fuel consumption rises 15-40%. If a mechanical issue forces you to run at less than full power, your fuel consumption changes unpredictably. The reserve third is there for exactly these situations.
Why GPH Changes Dramatically With Throttle Setting
The relationship between throttle and fuel burn is highly non-linear on planing hull boats. A 300 HP outboard running at wide-open throttle might burn 30 gallons per hour. At 70% throttle (cruise), the same engine might burn 16-18 GPH while only losing 20-25% of top speed. Throttle back to 50% and the burn drops to 8-10 GPH while still making reasonable headway at 60-65% of top speed. This is the throttle optimization concept: for most planing hull boats, backing off from WOT to efficient cruise dramatically extends range while sacrificing relatively little time on longer trips.
The throttle optimization table in Mode 1 of this calculator shows you GPH, NMPG, and safe range at five different throttle settings based on your engine setup. For most boaters planning offshore trips, the 70% cruise setting represents the sweet spot where the engine is fully out of the “displacement mode” hole and running efficiently on plane, but not burning the extra fuel required to push significantly past that speed. The efficiency curve levels off considerably above 70-80% throttle on most planing hulls.
Three Real US Boating Scenarios Calculated
Scenario 1: Center Console Offshore Trip, Cape Hatteras to the Gulf Stream
A 26-foot center console with twin Yamaha F250 outboards (500 HP total) has a 150-gallon tank. The captain wants to run 55 nautical miles offshore to the Gulf Stream edge in moderate seas (3-5 ft), then troll at 8 knots for 4 hours before running home in calmer conditions.
Leg
Distance / Activity
Speed
GPH (est.)
Fuel Used
Leg 1: Run offshore
55 nm, moderate seas
22 kts
500 x 0.10 x 0.60 x 1.22 = 36.6 GPH
55/0.60 = 91.7 gal
Leg 2: Trolling
4 hrs at 8 kts
8 kts
500 x 0.10 x 0.30 x 1.00 = 15 GPH
4 x 15 = 60 gal
Leg 3: Return
55 nm, calm
25 kts
500 x 0.10 x 0.65 x 1.00 = 32.5 GPH
55/0.77 = 71.4 gal
Total
223 gal needed / 142.5 gal usable (95% of 150) = NO-GO. This trip requires refueling at the dock before the return run, or filing a float plan with a much smaller fishing area.
This is a critically important scenario because many center console owners underestimate how quickly trolling consumes fuel. At 15 GPH for 4 hours, trolling alone burns 60 gallons: 42% of the usable tank before factoring in the transit legs. The Multi-Leg Trip Planner in this calculator would flag each leg’s cumulative fuel burn and issue a NO-GO when the math does not work, preventing a dangerous situation 55 miles offshore.
Scenario 2: Great Lakes Trawler Passage, Chicago to Mackinac Island
A 42-foot diesel trawler with a single 230 HP diesel engine and a 400-gallon tank plans the annual Chicago to Mackinac run. Distance: approximately 290 nautical miles. Expected cruising speed: 8.5 knots at 65% throttle. The captain wants to know range, cost at $4.80/gal marine diesel, and whether a single-tank passage is feasible.
Calculation
Formula
Result
GPH at 65% throttle
230 HP x 0.055 gal/HP x 0.55 load
6.9 GPH
NMPG
8.5 kts / 6.9 GPH
1.23 nm/gal
Max range (dry tanks)
380 gal usable x 1.23 nm/gal
467 nm
Safe range (one-third rule)
467 nm x 2/3
311 nm
Fuel needed for 290 nm
290 nm / 1.23 nm/gal
235.8 gal
Fuel remaining after trip
380 – 235.8
144.2 gal (38% reserve)
Decision and cost
GO – 38% reserve exceeds the 33% one-third rule. Cost: 235.8 gal x $4.80 = $1,131.84 for the passage. Estimated time: 290 / 8.5 = 34.1 hours (plan for 2 nights underway).
This is where the diesel trawler absolutely shines: 1.23 NMPG at 8.5 knots is extraordinarily efficient compared to a planing hull doing 25 knots at 1.0 NMPG. The trade-off is time: 34 hours versus perhaps 12 hours for a fast sport cruiser. For voyaging boaters, the trawler’s range and fuel economy make passages like the Mackinac run genuinely feasible without refueling stops.
Scenario 3: Offshore Fishing Boat, Florida Keys Day Trip
A 32-foot sportfisher with twin 300 HP gasoline engines (600 HP total, 250-gallon tank) runs from Marathon to the humps at approximately 40 nautical miles offshore. The captain uses a digital fuel flow meter and knows his cruise burn is 28 GPH (14 GPH per engine) at 23 knots. Dock fuel is $5.20/gal.
Parameter
Calculation
Result
NMPG at cruise
23 kts / 28 GPH
0.82 nm/gal
One-way fuel (40 nm)
40 / 0.82
48.8 gal
Round trip fuel (transit only)
48.8 x 2
97.6 gal
Fishing (4 hrs at 8 GPH idle/drift)
4 hrs x 8 GPH
32 gal
Total fuel needed
97.6 + 32
129.6 gal
One-third reserve required
237.5 usable / 3
79.2 gal
Trip cost
129.6 gal x $5.20 = $673.92 for the full day trip. Reserve after trip: 237.5 – 129.6 = 107.9 gal (45% of usable). GO: Plenty of reserve.
Using a known GPH reading from the flow meter (28 GPH) rather than an HP-based estimate significantly improves accuracy. The HP-based formula would estimate: 600 HP x 0.10 x 0.65 = 39 GPH at cruise: 39% higher than the actual 28 GPH reading. This illustrates why a digital fuel flow meter is one of the most valuable instruments on a boat. The HP formula is a planning estimate when you have nothing else; your actual fuel flow reading is always more accurate for your specific boat, prop, hull condition, and load.
Three Expert Tips on Marine Fuel Planning for US Recreational Boaters
Tip 1: Backing Off Throttle Saves More Fuel Than You Think on Planing Hulls
Most planing hull boats have an efficiency sweet spot that sits just above their planing threshold, typically 60-75% of wide-open throttle. At this setting, the hull is fully on plane (no longer pushing through its bow wave), the propeller is operating in its most efficient pitch range, and aerodynamic drag has not yet become a dominant factor. Pushing past this point accelerates the cube of aerodynamic drag: going from 25 knots to 35 knots might only add 10 minutes on a 30-mile trip, but can double your fuel consumption for the entire passage.
A practical example: a twin-engine center console running at 30 knots burns 45 GPH for a NMPG of 0.67. Back off to 22 knots (about 73% throttle) and it burns 24 GPH for a NMPG of 0.92-37% better fuel economy at a speed that only adds 19 minutes to a 30-mile run. Over a full offshore day, that throttle adjustment saves 30-40 gallons of fuel and extends the range enough to consider destinations that would otherwise require a fuel stop. Use the throttle optimization table in Mode 1 to see exactly where your efficiency curve peaks.
Tip 2: Your Actual GPH Is More Reliable Than Any Calculator When Planning Offshore
Every engine, hull, propeller combination, and load is different. The HP-based GPH formula (1 gallon per 10 HP at WOT for gasoline) is a useful starting estimate, but real-world variation between boats of similar power can be 20-40%. A boat with a slightly too-large propeller, marine growth on the hull, a heavy cooler load, or a stiff headwind can burn significantly more than the formula predicts. If you have a digital fuel flow meter (Lowrance, Garmin, Suzuki, or stand-alone units like the Maretron), log your actual GPH at cruise RPM on three or four outings and average the readings.
Enter that known GPH directly in Mode 3’s Fuel Cost Estimator rather than relying on the HP estimate. The difference can be the margin between returning to the dock with a comfortable reserve and running dry 5 miles from the inlet. The US Coast Guard’s Boating Safety Division recommends that all offshore boaters file a float plan with someone ashore that includes planned departure time, destination, return time, and fuel capacity, exactly the kind of calculation this tool helps you complete.
Tip 3: Sea Conditions and Headwinds Are the Hidden Fuel Destroyers on Returns
Marine fuel consumption is not symmetric between going out and coming back if conditions change during the day. Afternoon thunderstorms are common in Florida, the Gulf Coast, and the Chesapeake Bay during summer months, they build during the afternoon heat and often produce 15-25 knot headwinds and 3-5 foot seas for the homeward run. The same trip that burned 40 gallons going out might burn 55-65 gallons coming back through those conditions.
The sea condition correction factors in this calculator (10% penalty for light chop, 22% for moderate, 38% for rough) are based on published marine engineering data for typical planing hull center console boats. Plan your fuel budget for the worst conditions you might reasonably encounter, not the best. If you planned with calm seas but hit moderate chop on the return, you have consumed fuel you did not budget. The one-third reserve is designed to absorb exactly this kind of variation, but only if you actually maintain it before leaving the dock. The Multi-Leg Trip Planner lets you enter different sea conditions for each leg, giving a more realistic picture of a trip where outbound conditions differ from return conditions.
16 FAQs on Boat Fuel Consumption, Range, and Marine Trip Planning
The standard rule of thumb for gasoline outboard and inboard engines is 1 gallon per hour per 10 horsepower at wide-open throttle. A 150 HP outboard burns approximately 15 GPH at WOT, a 300 HP twin burns 30 GPH total at WOT. At typical cruise throttle (65-75%), multiply by 0.55-0.65: a 150 HP outboard at cruise burns approximately 8-10 GPH. Marine diesel engines are more efficient: approximately 0.055 gallons per HP at WOT, or 0.03-0.04 GPH per HP at cruise. A 250 HP diesel at cruise might burn 8-10 GPH versus a 250 HP gasoline engine burning 14-16 GPH at the same cruise speed. Always verify against your actual fuel flow gauge readings at your typical cruise RPM, as real-world figures vary by 20-40% based on hull condition, propeller selection, and load.
Boat fuel economy measured in nautical miles per gallon (NMPG) varies dramatically by boat type. Displacement hull trawlers: 2-5 NMPG at slow displacement speeds (6-10 knots). Pontoon boats: 1-3 NMPG at typical cruise. Center console outboards (single engine): 1.5-3 NMPG at 20-25 knot cruise. Center console outboards (twin engine): 0.8-1.8 NMPG at 25-30 knot cruise. Offshore sport fishing boats (twin engines): 0.6-1.2 NMPG. Express cruisers (twin gasoline inboards): 0.5-1.0 NMPG. High-performance center consoles (triple or quad outboards): 0.4-0.9 NMPG at high speeds. By comparison, automobile fuel economy expressed as equivalent NMPG would be approximately 25 mpg (statute) x 1 nm/1.15 statute miles = 22 NMPG equivalent, dramatically better than any planing hull boat due to the much lower hydrodynamic drag of rubber on pavement versus hull through water.
The one-third fuel rule is a practical marine safety guideline: divide your usable fuel into thirds. Use the first third going to your destination. Use the second third to return home. Keep the final third as an emergency reserve for headwinds, unexpected detours, mechanical issues, or helping another boater. In mathematical terms: safe planning range = (usable fuel x 2/3) x NMPG. Your radius of action (how far out you can go on a point-to-point trip and return safely) = safe planning range / 2. For a 100-gallon tank with 1.5 NMPG: max range would be 150 nm, safe range is 100 nm (66 gal x 1.5), and radius of action is 50 nm. The US Coast Guard recognizes the one-third rule as a fundamental component of responsible float plan preparation for offshore passages.
GPH (gallons per hour) measures how much fuel the engine consumes per unit of time at a specific throttle setting and operating condition. GPH does not directly tell you how far you can go, a boat going fast burns more GPH but also covers more distance per hour. NMPG (nautical miles per gallon) measures how far the boat travels per gallon of fuel, combining speed and fuel burn into a single efficiency number. Formula: NMPG = speed in knots / GPH. Both metrics are useful: GPH tells you how quickly your tank is draining (useful for time-at-anchor or trolling calculations), while NMPG tells you how far you can travel per gallon (useful for range planning). Most boats reach peak NMPG at a specific throttle and RPM setting below WOT, this is the “efficiency sweet spot” that maximizes range per gallon.
Rough sea conditions significantly increase fuel consumption beyond calm water estimates. Typical increases over calm sea baseline: light chop (1-3 foot seas): 10-15% higher fuel burn, because the hull must work against the waves and the prop encounters variable load. Moderate seas (3-5 feet): 20-30% higher fuel burn, as the helmsman often backs off throttle to maintain a comfortable ride and the hull is periodically lifting out of the water. Rough seas (5-8 feet): 35-50% higher fuel burn, as the boat may be significantly slowed, spending more time at partial power or being driven on alternative headings to avoid beam seas. These factors are why a return trip against a building sea state after a day of fishing can consume dramatically more fuel than the outbound passage in the morning calm. This calculator applies 1.00, 1.10, 1.22, and 1.38 multipliers for calm, light, moderate, and rough conditions respectively.
The HP-based estimate (1 GPH per 10 HP at WOT for gasoline) is accurate within approximately 20-30% for most boats in good mechanical condition with properly sized propellers. Sources of variation: propeller selection has a significant effect, an under-pitched or over-pitched propeller causes the engine to work harder and burn more fuel at any given speed. Hull fouling from marine growth adds drag and can increase fuel consumption 10-20% compared to a freshly cleaned bottom. Cargo and passenger load affects fuel burn by approximately 5-10% for typical recreational loads. Engine condition and maintenance state also matter. For more accurate planning, use a digital fuel flow meter installed in the fuel line between the fuel tank and the engine. Garmin, Lowrance, Suzuki, Yamaha, Mercury, and third-party instruments like Navico all offer digital flow meters that display real-time GPH and cumulative consumption. After a few trips, you will have actual verified GPH data for your specific boat at typical cruise settings.
A float plan is a written document left with a responsible person ashore (not on the water with you) that describes your trip: vessel description, registration number, departure point and time, planned destination, planned route, expected return time, number of people aboard, emergency contact information, and your vessel’s fuel capacity and estimated range. If you do not return or check in by the specified time, the person holding the float plan calls the US Coast Guard to initiate a search. Float plans are not filed with the Coast Guard directly, they are left with marina staff, family, or friends who can take action if you do not return. The US Coast Guard provides a standard float plan form at uscgboating.org. Using this calculator to confirm your fuel range before departure gives you the numbers you need to fill out the range and expected route section of a proper float plan.
Marine fuel prices at marinas typically run $0.50 to $1.50 per gallon above roadside pump prices due to marina overhead, dock labor, fuel dock insurance, and smaller delivery volumes. As of mid-2025, typical US marine gasoline (87 octane or ethanol-free marine premium) ranges from $4.50 to $7.00 per gallon depending on location. The Florida Keys, offshore Bahamas-adjacent marinas, and remote Pacific Northwest locations tend to have the highest prices. Marine diesel follows a similar premium over roadside diesel prices. For most bluewater cruisers with diesel trawlers, the combination of lower per-gallon price and significantly better fuel efficiency (0.055 vs 0.10 GPH per HP) makes diesel dramatically cheaper per nautical mile traveled compared to gasoline power. A long-range diesel trawler might spend $600-$900 on fuel for a 300-mile passage where a similar-sized gasoline sportfisher could spend $1,500-$2,500 for the same distance.
Twin outboards burn roughly twice the fuel of a single engine of the same total horsepower at any given throttle setting, because you are running two powerheads, two sets of fuel injectors, and two combustion cycles. A single 300 HP outboard and twin 150 HP outboards produce similar theoretical thrust, but the single engine typically has slightly lower mechanical losses at cruise. In practice, twin engine installations are preferred for offshore use because of the redundancy, if one engine fails, you can return on the other. For fuel planning purposes, this calculator multiplies the per-engine HP by the number of engines when estimating total GPH. A boat with twin 250 HP outboards running at 65% throttle would have an estimated total GPH of: 2 engines x 250 HP x 0.10 gal/HP x 0.60 load = 30 GPH total. Running on a single engine for the return in an emergency would cut consumption to approximately 15 GPH at reduced speed.
Hull speed (also called displacement speed) is the theoretical maximum speed a displacement hull can travel before the bow wave energy requirement grows exponentially: hull speed in knots = 1.34 x square root of waterline length in feet. A 40-foot trawler with a 36-foot waterline has a hull speed of approximately 8 knots. At or below hull speed, a displacement hull pushes through the water very efficiently, the bow wave does not build ahead of the vessel and resistance is primarily frictional. Above hull speed, a displacement hull requires exponentially more power to climb over its own bow wave, consuming enormous fuel. Planing hulls overcome this limitation by generating lift at higher speeds, literally rising up and skimming on top of the water surface rather than pushing through it. The trade-off is that achieving planning requires significantly more initial power and fuel. The result is that a 40-foot diesel trawler running at 8 knots achieves 2-3 NMPG, while a 40-foot sportfisher running at 28 knots achieves 0.8-1.2 NMPG, the trawler gets 2-3 times better fuel economy by operating in an entirely different physical regime.
Most marine engine manufacturers strongly recommend or require ethanol-free fuel for several reasons. Ethanol is hygroscopic, it absorbs water from the atmosphere. In a marine environment with high humidity and vessels that may sit for weeks between uses, ethanol-blended fuel (E10, with 10% ethanol) can absorb enough water to phase-separate: the ethanol and water layer settles to the bottom of the tank while the gasoline floats on top. The water-ethanol mixture drawn into the engine causes rough running, misfires, and potentially internal corrosion. Fiberglass tanks and older rubber fuel lines can also degrade with prolonged ethanol exposure. Ethanol-free marine premium (also labeled as E0 or recreational fuel) is available at most marine fuel docks at a premium over E10 pump prices. For fuel consumption purposes, ethanol-blended fuel has approximately 3% lower energy content than ethanol-free gasoline, which would theoretically increase GPH by about 3% for the same power output, a minor but measurable effect on long passages.
Outboard and sterndrive trim angle has a significant effect on fuel consumption and range. Trimmed too far in (bow down): the hull plows through the water with the bow low, creating excessive bow wave drag and burning 15-25% more fuel than optimal. Trimmed too far out (bow up, over-trimmed): the propeller ventilates (sucks air), loses grip, and the hull rides inefficiently on the stern. Properly trimmed for cruise: the hull runs on its designed running strake, the prop is fully loaded, and resistance is minimized. Finding the proper trim for cruise typically involves adjusting the trim tabs or outboard trim while watching the tachometer and speedometer, you are looking for the highest speed at a fixed throttle setting, or lowest RPM at a fixed target speed. Many modern outboard-equipped boats can find 0.2-0.4 NMPG improvement simply through proper trim adjustment, which can add 20-40 miles of range on a 100-nm trip. This is a free optimization available to every boater before ever buying a fuel-saving propeller or throttle-back technique.
1 knot = 1 nautical mile per hour = 1.15078 statute miles per hour. To convert knots to mph: multiply knots by 1.151 (or 1.15 for practical purposes). Common conversions: 10 knots = 11.5 mph, 20 knots = 23.0 mph, 25 knots = 28.8 mph, 30 knots = 34.5 mph, 40 knots = 46.0 mph. A nautical mile is defined as exactly 1,852 meters or approximately 6,076 feet, compared to a statute mile of exactly 5,280 feet. The US Coast Guard, NOAA, and all nautical charts and GPS chartplotters express distances in nautical miles and speeds in knots. If you are more familiar with statute miles and mph, you can convert your boat’s GPS speed reading (typically in knots) to mph by multiplying by 1.15. This calculator uses knots throughout because all marine navigation and weather forecasting in the US uses the nautical mile and knot system.
Fuel tank capacity for center console fishing boats scales approximately with boat length and target offshore range. Common US center console fuel capacities: 20-22 ft (small): 50-75 gallons. 24-26 ft (mid-size offshore): 100-150 gallons. 28-32 ft (offshore): 150-250 gallons. 35-38 ft (dedicated offshore): 250-400 gallons. 40+ ft (long-range): 400-800+ gallons. Some dedicated offshore boats in the 32-38-foot range (Contender, Yellowfin, Boston Whaler Outrage) offer optional extended fuel tanks that can push capacity to 400+ gallons, enabling two-day offshore runs to the Gulf Stream or Bahamas without refueling. When comparing boats, consider the range per dollar of additional fuel tank capacity against the weight penalty, every additional gallon of fuel weighs about 6.1 pounds for gasoline, and a 50-gallon auxiliary tank adds 305 pounds to the vessel displacement.
Tidal and ocean currents can significantly affect both speed over ground (SOG) and fuel consumption. A 2-knot favorable current behind a boat running at 20 knots gives 22 knots of SOG while burning fuel at the same rate as 20 knots through the water, effectively improving NMPG by 10%. A 2-knot adverse current forces the engine to work at 22 knots through the water to make 20 knots of SOG, burning significantly more fuel for the same ground distance. For trip planning on tidal waterways like the Chesapeake Bay, Long Island Sound, or Florida’s Intracoastal Waterway, checking NOAA tidal current predictions can save significant fuel by timing passages to run with favorable currents. The NOAA Tides and Currents database at tidesandcurrents.noaa.gov provides tidal current predictions for most US coastal waters. On offshore passages, checking NOAA ocean current charts for Gulf Stream position helps plan routes that use or avoid the 3-4 knot Gulf Stream current, which can dramatically affect fuel consumption and transit times for passages along the US East Coast.
TowBoat US and Sea Tow are the two major US commercial on-water towing and assistance services, similar to AAA for automobiles. They provide towing for mechanical breakdowns, fuel delivery to boats that run out of fuel, anchor assistance, and soft ungrounding. Annual membership typically costs $150-$250 and covers unlimited towing within certain geographic limits. Running out of fuel is one of the most common calls they receive, and also one of the most preventable, which is why this calculator emphasizes the one-third rule so prominently. Having TowBoat US or Sea Tow membership is a sensible backup for any offshore boater, but it is not a substitute for proper fuel planning. A fuel delivery service call typically takes 1-2 hours to arrive, during which time you are adrift and potentially in a shipping lane or deteriorating weather. Proper fuel planning with the one-third reserve maintained eliminates this risk entirely. BoatUS also publishes extensive boating safety resources at boatus.org.
Fuel consumption estimates use the standard marine rule of thumb: 1 gallon per hour per 10 HP at WOT for gasoline engines (0.055 GPH/HP for diesel), with throttle load factors of 1.00 (WOT), 0.75 (80%), 0.60 (70% cruise), 0.45 (60%), and 0.30 (50%). Sea condition multipliers of 1.00, 1.10, 1.22, and 1.38 are applied for calm, light chop, moderate, and rough conditions. These are representative estimates for typical planing hull center console boats; actual consumption varies significantly by hull design, propeller selection, engine maintenance, weight, and sea conditions.
The one-third reserve rule is a widely recognized best-practice guideline, not a US Coast Guard regulatory requirement for recreational vessels. However, operating with adequate fuel reserves is your legal responsibility as a vessel operator. Always verify fuel level before departure with your fuel gauges. Never plan a trip that requires running to empty tanks. This calculator is a planning tool only, always exercise caution and maintain additional reserves for offshore or remote passages. File a float plan with someone ashore before any offshore trip. Editorial transparency: No marine equipment manufacturer, fuel company, or marina paid to influence the content, formulas, or recommendations on this page. All engineering estimates are derived from publicly available marine engine performance data.