Fuel Pump Calculator

Estimate the fuel flow your engine needs at full power and the minimum pump rating — in lb/hr, gal/hr, and liters/hour — required to supply it, based on horsepower, brake specific fuel consumption (BSFC), fuel type, and pump duty cycle.

Quick Facts

Core formula
Required flow = HP x BSFC (lb/hr)
BSFC is fuel burned per horsepower per hour; naturally aspirated gasoline engines typically run 0.45-0.55 lb/hp-hr, boosted engines often need 0.55-0.65 lb/hp-hr.
Duty cycle margin
Pumps are sized above the raw requirement
Running a pump near 100% duty cycle shortens its life and lets voltage sag cut flow, so most tuners size for about 80% max duty cycle at full load.

Your Results

Calculated
Required fuel flow
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HP x BSFC at full power
Required flow (gal/hr)
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Volumetric flow at fuel density
Minimum pump rating
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Sized for target duty cycle
Minimum pump rating (lph)
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Compare to manufacturer flow specs

Ready

Enter horsepower, BSFC, fuel type, and duty cycle, then press Calculate.

About the Fuel Pump Calculator

This tool estimates how much fuel an engine needs at full power and translates that into the minimum flow rating a fuel pump must carry to supply it safely. It uses the standard automotive tuning method built on brake specific fuel consumption (BSFC), a duty cycle margin, and fuel density — the same building blocks used by aftermarket fuel system suppliers when they recommend a pump for a given power goal.

The formulas

Four calculations happen in sequence:

  • Required fuel flow (lb/hr): engine horsepower multiplied by BSFC — flow = HP × BSFC. BSFC (brake specific fuel consumption) is the mass of fuel burned per horsepower per hour, typically 0.45-0.55 lb/hp-hr for naturally aspirated gasoline engines and 0.55-0.65 lb/hp-hr for turbocharged or supercharged engines running richer under boost.
  • Required flow (gal/hr): the lb/hr figure divided by the fuel's density in lb per gallon. This calculator uses approximate densities of 6.15 lb/gal for gasoline, 6.50 lb/gal for E85, and 7.10 lb/gal for diesel; actual density varies with blend and temperature.
  • Minimum pump rating (lb/hr): the required flow divided by your target duty cycle (default 80%). A pump run at 100% duty cycle continuously has no margin for battery voltage sag and wears out faster, so sizing it to reach only 80% of its capacity at your power goal leaves headroom.
  • Minimum pump rating (lph): the minimum lb/hr figure converted to liters per hour, since aftermarket pumps (Walbro, Bosch, DeatschWerks, and similar) are almost always advertised by their lph rating at a stated test pressure.

Worked example

A 400 hp naturally aspirated engine with a BSFC of 0.50 lb/hp-hr needs 400 × 0.50 = 200 lb/hr of gasoline, or 200 / 6.15 ≈ 32.5 gal/hr. Sized to 80% max duty cycle, the pump must be rated for at least 200 / 0.80 = 250 lb/hr, which is 250 / 6.15 ≈ 40.7 gal/hr, or 40.7 × 3.785 ≈ 154 lph — within reach of many higher-flow stock and entry-level aftermarket in-tank pumps.

Why duty cycle and fuel pressure both matter

The lph number on a pump's box is measured at a specific test pressure, commonly 3 bar (43.5 psi). Real flow falls as fuel pressure rises above that point and rises as pressure falls below it, so a pump that just clears the calculated minimum at the manufacturer's test pressure can fall short once boost-referenced fuel pressure climbs. Treat the result here as the floor to shop against, not the final word — always check the pump's published flow curve at your actual target pressure.

Frequently Asked Questions

What formula does this fuel pump calculator use?
Required fuel flow equals horsepower multiplied by brake specific fuel consumption (BSFC): flow (lb/hr) = HP x BSFC. That figure is converted to gallons per hour using the fuel's density, then divided by your duty cycle target to get the minimum pump rating, which is converted to liters per hour (lph) since most aftermarket pumps are rated that way.
What BSFC value should I use?
BSFC is fuel burned per horsepower per hour. Naturally aspirated gasoline engines typically run about 0.45 to 0.55 lb/hp-hr, while turbocharged or supercharged engines run richer under boost, often 0.55 to 0.65 lb/hp-hr. Use a dyno-logged value for your specific combination when you have one; otherwise these ranges are reasonable planning defaults.
Why size the pump above the calculated flow requirement?
Running a pump at or near 100% duty cycle continuously shortens its service life and leaves no margin for battery voltage sag, which reduces output. Most tuners target roughly 80% maximum duty cycle at full load, so the calculator divides the raw requirement by that duty cycle to get the minimum pump rating to shop for.
Does fuel pressure affect a pump's rated flow?
Yes. Manufacturer lph ratings are measured at a specific test pressure, commonly 3 bar (43.5 psi). Flow drops as pressure rises above that point and rises as pressure falls below it, so a pump that meets the calculated minimum at the test pressure can fall short at a higher rail pressure, particularly under boost with a 1:1 rising-rate regulator.

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