Fuel pump flow calculator
How much fuel your engine burns at full power, in gallons and liters per hour, and the pump rating that covers it with a safety margin.
Pump flow needed
- In gallons per hour
- –
- Fuel burned at full power
- –
- Without the margin
- –
Pumps are rated at a specific pressure and voltage, and flow drops as pressure rises. Check the pump's flow chart at your actual fuel pressure, adding boost if the regulator is boost-referenced.
How pump flow is calculated
Gallons per hour = lb/hr ÷ fuel weight per gallon
Liters per hour = gallons per hour × 3.785
BSFC is how many pounds of fuel the engine burns per horsepower per hour. The defaults match the fuel injector calculator: about 0.50 for naturally aspirated gasoline, 0.60 boosted, 0.70 on E85 and 0.80 on boosted E85. Gasoline weighs about 6.1 lb per gallon and E85 about 6.6.
The margin covers pump wear, heat and voltage drop. Many builders size for 20 to 30% more than the engine needs.
Frequently asked questions
Why do I need a safety margin above my calculated fuel need?
Fuel pumps lose flow capacity as system pressure rises and as they age, and running a pump right at its rated capacity with zero headroom risks fuel starvation under real driving conditions — a safety margin covers both of those real-world losses.
Does this account for boosted engines needing more fuel?
Yes — the underlying horsepower-to-fuel-flow relationship (through BSFC) scales with the power level you enter, so a boosted engine's higher horsepower number naturally produces a correspondingly higher fuel flow requirement without needing a separate boost adjustment.
What BSFC number should I use for my engine?
A naturally aspirated gasoline engine commonly runs around 0.45-0.50 lb/hp/hr, while boosted or less efficient combinations run higher — using a BSFC that's too optimistic will undersize your fuel system, so lean toward a conservative number if you're unsure.
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