Fuel Pump Calculator (required pump flow in L/h & gal/h from horsepower)

Understanding the fuel pump calculator — concept and principle

This calculator estimates how much flow a fuel pump must deliver to support a target engine power. It works from brake-specific fuel consumption (BSFC), fuel density and a safety margin, and gives the answer in litres and US gallons per hour. Tuners use it when choosing an in-tank or inline pump for a power upgrade.

Power times BSFC gives fuel mass; density turns it into volume, and the margin covers pressure and voltage losses.

How it is calculated

Fuel burned (lb/h) = power (hp) × BSFC (lb/hp·h)

Fuel burned (L/h) = lb/h × 0.45359237 ÷ density (kg/L)

Pump flow needed = fuel burned × (1 + margin)

Power in kW is converted to hp (1 hp = 0.7457 kW). 1 US gal = 3.785411784 L.

The principle

BSFC tells you how much fuel an engine burns per unit of power per hour. Multiplying by the target power gives the mass of fuel the engine consumes at full load. A pump moves volume, so the mass is divided by density. The margin covers what the simple sum leaves out: pump wear, low supply voltage, filter restriction and, on boosted engines with a 1:1 regulator, the higher fuel pressure under boost, which reduces what a pump can deliver.

Worked example

Default inputs: 400 hp, BSFC 0.55, density 0.745 kg/L, margin 20%.

Fuel burned = 400 × 0.55 = 220 lb/h = 220 × 0.45359 = 99.8 kg/h.
In litres = 99.79 ÷ 0.745 = 133.9 L/h.
With 20% margin = 133.94 × 1.2 = 161 L/h.
In US gallons = 160.7 ÷ 3.785 = 42.5 gal/h.

Each point is the calculator re-run with only “Fuel density (kg/L)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Fuel density (kg/L)	Pump flow needed (L/h)
0.186	643
0.372	321
0.559	214
0.745	161
0.931	129
1.12	107
1.49	80

How to read the result

Compare the required flow with the pump's rated flow at your actual fuel pressure and voltage, not the free-flow figure on the box. Pump curves fall as pressure rises, so a pump that flows 255 L/h at 3 bar may deliver much less at the pressure a boosted engine needs. Garrett gives typical BSFC values of about 0.50–0.60 lb/hp·h for turbocharged petrol engines.

Common mistakes

Reading the pump's free-flow rating instead of the flow at operating pressure.
Ignoring voltage drop in the wiring, which reduces pump speed and flow.
Using wheel power instead of crank power.
Using petrol figures for ethanol blends, which need far more fuel.

Keep in mind: This is an educational estimate. Confirm pump selection with the manufacturer's flow curves and have fuel-system work done by a qualified professional.

Frequently asked questions

Why add a safety margin?

Pumps wear, voltage sags and filters clog, so running a pump at its limit risks a lean condition at full power.

Does boost pressure affect pump flow?

Yes. With a rising-rate regulator the pump must work against higher pressure under boost, so its flow drops.

What fuel density should I use?

Petrol is commonly taken as about 0.72–0.76 kg/L; check the figure for your fuel.

Sources: Garrett Motion, "How to Select a Turbo, Part 2" (BSFC values) · C. Shih, "Internal Combustion Engines" lecture notes, FAMU–FSU College of Engineering

Checked 9 Nov 2026. Garrett Motion, “How to Select a Turbo, Part 2”: BSFC values for turbocharged petrol engines (about 0.50–0.60 lb/hp·h); fuel flow = power × BSFC (definition of BSFC, C. Shih, “Internal Combustion Engines” lecture notes, FAMU–FSU). 1 lb = 0.45359237 kg, 1 US gal = 3.785411784 L.

Your numbers