Boat Fuel Calculator
Boat Fuel Consumption by Engine HP (Gasoline, 75% Throttle)
Estimated GPH and range at cruising speed.
| Engine HP | GPH | At 20 kts (NMPG) | 30-gal Range | 50-gal Range |
|---|---|---|---|---|
| 40 HP | 3.0 | 6.7 | 200 nm | 333 nm |
| 75 HP | 5.6 | 3.6 | 107 nm | 179 nm |
| 115 HP | 8.6 | 2.3 | 70 nm | 116 nm |
| 150 HP | 11.3 | 1.8 | 53 nm | 89 nm |
| 200 HP | 15.0 | 1.3 | 40 nm | 67 nm |
| 250 HP | 18.8 | 1.1 | 32 nm | 53 nm |
| 300 HP | 22.5 | 0.9 | 27 nm | 44 nm |
| 350 HP | 26.3 | 0.8 | 23 nm | 38 nm |
| Twin 150 HP | 22.5 | 0.9 | 27 nm | 44 nm |
| Twin 250 HP | 37.5 | 0.5 | 16 nm | 27 nm |
How We Calculate This
This boat fuel calculator uses established formulas and industry-standard data to provide accurate estimates.
- Enter your specific values into the calculator fields above
- Our algorithm applies the relevant formulas using your inputs
- Results are calculated instantly in your browser — nothing is sent to a server
- Review the detailed breakdown to understand how each factor affects your result
These calculations are estimates based on standard formulas. For critical decisions, always consult a qualified professional.
How to Convert Oven Recipes to Air Fryer
Boat fuel consumption depends on engine horsepower, fuel type, and throttle setting. The standard rule of thumb uses a simple HP-based formula.
The basic rule:
- Gasoline engines: GPH = HP × 0.10 at full throttle
- Diesel engines: GPH = HP × 0.055 at full throttle
- Fuel needed = GPH × (distance / speed). Always add a 10% safety reserve
These are estimates based on rule-of-thumb calculations. Actual consumption varies with hull design, load, sea conditions, and engine efficiency. Always carry more fuel than calculated, especially offshore.
When Would You Use This Calculator?
This boat fuel calculator is designed for anyone who needs quick, reliable estimates without complex spreadsheets or professional consultations.
- When you need a quick estimate before committing to a purchase or project
- When comparing different options or scenarios side by side
- When planning a budget and need to understand potential costs
- When you want to verify a quote or estimate you've received from a professional
- When teaching or learning about the concepts behind these calculations
Frequently Asked Questions
How do I calculate boat fuel consumption?
For gasoline engines, multiply HP by 0.10 to get gallons per hour at full throttle. For diesel, multiply by 0.055. Then multiply GPH by the number of hours your trip will take (distance / speed). Always add a 10% safety reserve.
How much fuel does a 150 HP outboard use?
A 150 HP gasoline outboard at full throttle uses about 15 gallons per hour (150 × 0.10). At cruising speed (75% throttle), consumption drops to about 11.25 GPH. At trolling speed (50%), it's about 7.5 GPH.
What is the 1/3 fuel rule for boats?
The rule of thirds says: use 1/3 of your fuel to go out, 1/3 to come back, and keep 1/3 in reserve. This calculator uses a 10% reserve which is the minimum — the 1/3 rule is more conservative and recommended for offshore trips or unfamiliar waters.
How far can a boat go on a tank of gas?
Range = tank capacity × nautical MPG. For example, a boat with a 100-gallon tank getting 2 NMPG has a range of 200 nautical miles. At 75% throttle with a 150HP engine, that's about 100 gallons / 11.25 GPH × 20 knots = 178 nm.
Does speed affect fuel consumption?
Yes, dramatically. Most boats have a sweet spot around 60-75% throttle where fuel efficiency is best. At wide open throttle, fuel consumption can increase 50-100% while speed only increases 20-30%. Planing hulls are most efficient at or just above planing speed.
Is diesel more fuel efficient than gas for boats?
Yes. Diesel engines use roughly 55% less fuel per HP than gasoline engines (0.055 vs 0.10 GPH/HP). Diesel fuel also has more energy per gallon. However, diesel engines cost more upfront. For boats used frequently or over long distances, diesel saves significantly on fuel costs.