Calculate fuel pump flow rate, pressure requirements, and sizing for automotive and marine engines. Match pump capacity to horsepower demands.
Selecting the right fuel pump is critical for engine performance and reliability. An undersized pump starves the engine of fuel at high loads, causing lean conditions and potential damage. An oversized pump wastes energy and can create fuel-management headaches. This calculator helps you size a fuel pump correctly based on your engine's horsepower target, BSFC, and fuel system pressure.
For naturally aspirated engines, fuel demand is straightforward: multiply target horsepower by BSFC and add a safety margin. For forced-induction setups (turbo or supercharged), you must account for the boost pressure the pump works against, which reduces effective flow. Our calculator handles both cases and converts between gallons per hour (GPH), liters per hour (LPH), and cc/min.
Whether you're upgrading a street car, building a race engine, or specifying a marine fuel system, this tool gives you the exact pump capacity you need. The reference table shows popular aftermarket pumps with their rated flows at various pressures, so you can quickly match specs.
Use this calculator to match pump flow to the fuel demand your engine actually has at operating pressure. That helps prevent lean conditions from an undersized pump and avoids the extra heat, wiring load, and regulator bypass issues that come with oversizing. It is especially useful when comparing gasoline, E85, EFI, and boosted setups.
Required fuel flow (lb/h) = Target HP × BSFC (lb/hp·h). Flow in GPH = lb/h ÷ 6.17 (gasoline). Flow in LPH = GPH × 3.78541. Effective flow under boost: pump must overcome base pressure + boost pressure.
Result: 48.9 GPH / 185.1 LPH required
At 400 HP with 0.50 lb/hp·h BSFC, fuel demand is 200 lb/h = 32.4 GPH at base pressure. With 15 PSI boost, the pump must deliver at 58.5 PSI total. Adding 15% margin: 37.3 GPH base → 48.9 GPH at operating pressure.
Electric fuel pumps use a DC motor to spin an impeller or gear set that pressurizes fuel from the tank to the engine's fuel rail. Flow rate decreases as outlet pressure increases — this is why pump specs always include a pressure rating. A pump rated at 255 LPH at 40 PSI might only deliver 200 LPH at 60 PSI.
Turbocharged and supercharged engines present a unique challenge: the fuel rail pressure must be maintained above manifold pressure for injectors to operate. A "rising-rate" fuel pressure regulator adds 1:1 PSI with boost. At 15 PSI of boost with a 43.5 PSI base, the pump sees 58.5 PSI — significantly reducing flow versus its label rating.
The Walbro 255 (GSS342) is one of the most popular OEM-replacement performance pumps. It flows approximately 255 LPH at 40 PSI but only 190 LPH at 80 PSI. The AEM 50-1000 flows 320 LPH at 40 PSI. For serious builds (800+ HP), the DW400 at 415 LPH or dual pump setups are common.
For gasoline engines: 0.45–0.55 lb/hp·h (use 0.55 for safety). For E85: 0.65–0.75 lb/hp·h. Diesel: 0.35–0.42 lb/hp·h.
The pump must push fuel against injector rail pressure. With boost, rail pressure equals base pressure + boost. Higher pressure reduces pump volume flow, so you need a larger pump.
Always. A pump running at 100% capacity overheats and fails prematurely. Size for at least 10–15% over calculated demand.
Free-flow is at 0 PSI — meaningless for real applications. Rated flow at a specific pressure (e.g., 255 LPH @ 43.5 PSI) is what matters.
Yes, but the fuel pressure regulator must bypass excess flow. Very oversized pumps waste electrical power and generate unnecessary heat in the fuel.
EFI systems run 40–60 PSI and need high-pressure pumps (typically in-tank). Carbureted engines need only 4–7 PSI but higher volume per PSI.