Fuel Tank Capacity Calculator 🛢️
Calculate your boat's fuel tank volume in US gallons and liters. Supports rectangular and cylindrical tank shapes. Enter dimensions in inches.
How to Use the Fuel Tank Capacity Calculator
Select your tank shape (rectangular or cylindrical), enter inside dimensions in inches, and the calculator computes volume in US gallons and liters. 1 US gallon = 231 cubic inches.
Rectangular: Volume = L × W × H. Cylindrical (horizontal): Volume = π × (D/2)² × L. Measure inside dimensions for accuracy.
Leave 5–10% ullage (air space) for fuel expansion — never fill a marine fuel tank 100% full. Overfilling causes fuel to overflow through the vent, creating fire and environmental hazards.
Boat & Marine Calculator - Introduction
Measure your tank's interior dimensions in inches and select rectangular or cylindrical shape to get the usable capacity in US gallons and liters. The tool also shows the 90–95% fill level, which is the safe working capacity after leaving 5–10% ullage for thermal expansion of fuel.
How It Works
Rectangular volume (cu in) = L × W × H; cylindrical volume (cu in) = π × (D/2)² × length. Both divide by 231 to get US gallons (1 US gallon = 231 cu in exactly), then multiply by 3.78541 for liters. Example: a 36 × 14 × 10-inch rectangular tank = 5040 cu in ÷ 231 = 21.8 gallons; 90% fill = 19.6 gallons safe working capacity.
Usage Scenarios
- Verifying range before a long coastal run: A 26-ft cruiser has a tank measured at 30 × 12 × 10 inches = 3600 cu in ÷ 231 = 15.6 gallons. At a cruise burn of 5 GPH, that's about 3 hours of fuel—not enough for a planned 80-nm trip. The owner decides to add a secondary tank before departure.
- Replacing a corroded tank with a custom fit: A boatyard is fabricating a new aluminum tank to fit an awkward 42 × 16 × 8-inch bilge space. The calculator returns 46.6 gallons usable at 95% fill, which the owner confirms is enough for a full offshore day before ordering materials.
- Cross-checking a seller's spec sheet: A buyer is told a used 28-ft boat has a 50-gallon tank. Measuring the hatch reveals a 38 × 18 × 12-inch cavity = 8208 cu in ÷ 231 ≈ 35.5 gallons. The discrepancy prompts a closer inspection of whether a second tank exists or the listing was inaccurate.
Frequently Asked Questions
How do I calculate boat fuel tank capacity?
Rectangular: Volume (cu in) = L × W × H, then divide by 231 for US gallons. Cylindrical: Volume (cu in) = π × (D/2)² × Length, then divide by 231. All measurements in inches. 1 US gallon = 231 cubic inches.
How full should I fill a marine fuel tank?
Fill marine fuel tanks to 90–95%, leaving 5–10% ullage for thermal expansion. Overfilling causes fuel to overflow through the vent, creating fire and environmental hazards. Use a slow fill rate near the top.
How do I convert cubic inches to gallons?
Divide cubic inches by 231. Example: a 24" × 12" × 10" tank = 2880 cu in ÷ 231 = 12.5 US gallons. Multiply gallons by 3.785 to convert to liters.
What is the typical fuel tank size for a recreational boat?
Small runabouts (16–20 ft): 15–40 gallons. Mid-size boats (20–25 ft): 50–100 gallons. Larger cruisers (25–35 ft): 100–300 gallons. Center consoles vary widely. Check your owner's manual for the exact capacity.