Boat Fuel Consumption Chart by Horsepower and RPM (L/h & GPH)

Introduction

Fuel consumption is one of the biggest ongoing costs for any boater — and it varies dramatically based on engine horsepower, RPM, and load. Understanding these relationships can help you plan trips more safely, calculate your range more accurately, and even lower your annual fuel bill.

This guide provides a quick reference chart for both gasoline outboards and diesel inboards. It's based on practical data compiled from marine engine studies and field reports, including the Brake-specific fuel consumption and manufacturer data from Mercury Marine, Yamaha, and Volvo Penta.

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⚙️ Why Fuel Burn Varies So Much

Before jumping into the numbers, it’s worth understanding the main variables affecting fuel consumption:

1. RPM (Revolutions per minute) – Higher RPM increases both fuel flow and drag exponentially.
2. Engine Load – Extra passengers, cargo, or gear can increase fuel burn by 10–20%.
3. Hull Design – Planing hulls burn more fuel at low speeds; displacement hulls are more consistent.
4. Trim & Sea State – Poor trim or rough conditions can easily add 15% to hourly consumption.
5. Maintenance – Fouled propellers or clogged filters can waste up to 25% more fuel according to engine efficiency.

These factors mean that your real-world burn rate might differ from the theoretical numbers — but charts are still incredibly useful for ballpark estimates and trip planning.

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⛽ Typical Gasoline Outboard Fuel Consumption Rates

These values assume a four-stroke outboard engine operating at 70–80% throttle — the efficiency "sweet spot" recommended by BoatUS Foundation.

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⚙️ Diesel Inboard Fuel Consumption Rates

Diesel engines are about 15–25% more efficient than gasoline counterparts. Their fuel burn rate averages 0.20 L/h per HP, compared to 0.24 L/h per HP for gasoline engines.

This efficiency gap becomes significant for longer passages, where a 300 HP diesel can save over $1,000 per season in fuel.

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📈 How to Use the Chart for Trip Planning

Let’s say you have a 200 HP outboard that burns 36 L/h at 4000 RPM and your average cruising speed is 25 knots. Your 200-liter fuel tank gives you:

Range (NM) = (Fuel Capacity / L/h) × Speed Range = (200 / 36) × 25 ≈ 138 NM

That’s a 138-nautical-mile range under ideal conditions — before accounting for a 10–20% safety margin.

You can check this automatically using our Fuel Range Calculator, which visualizes distance and reserve fuel in multiple units (NM, miles, kilometers).

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🧮 Need Brand-Specific Data?

Fuel efficiency varies by manufacturer and model. For exact data and real-world test figures, see our dedicated Mercury calculators:

• Mercury 400 V10 Calculator
• Mercury 500R Calculator
• Mercury 600 V12 Calculator

Each calculator uses published horsepower curves and burn rate charts to estimate hourly fuel use in both L/h and GPH, based on factory data from Mercury Marine's official specifications.

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⚡ Expert Insight: Understanding “GPH” vs “L/h”

Many U.S. boaters use GPH (gallons per hour), while European and Australian charts favor L/h (liters per hour). Both are just flow rate units, and you can convert easily:

1 GPH = 3.785 L/h 1 L/h = 0.264 GPH

For performance tracking, keep records in whichever system matches your local fuel pricing — most fuel receipts list gallons in the U.S. and liters elsewhere.

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✅ Conclusion

Fuel consumption charts are great starting points for understanding your boat’s performance envelope. They help estimate range, plan refueling stops, and compare different engines or cruising speeds.

Still, nothing beats measuring your real burn rate over time. Record your fuel use per trip, monitor your RPM vs. GPS speed, and compare results with tools like our Boat Fuel Consumption Calculator.

With consistent logging and awareness, you’ll not only save fuel — you’ll gain confidence in your boat’s true range and efficiency.

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Sources:

• Improving Your Boat's Fuel Efficiency - Mercury Marine
• Brake-specific fuel consumption
• BoatUS Foundation – Fuel-Saving Tips for Boaters
• Mercury Marine – Outboard Engine Specs