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?
What BSFC value should I use?
Why size the pump above the calculated flow requirement?
Does fuel pressure affect a pump's rated flow?
Common Tip Percentages
| Service | Typical Tip Range | Notes |
|---|---|---|
| Restaurant (sit-down) | 15–20% | 20%+ for exceptional service |
| Food delivery | 10–20% | Consider extra for long distances |
| Taxi / rideshare | 10–20% | More for assistance with luggage |
| Hotel housekeeping | $2–5/night | Leave daily, not just at checkout |
| Barber / hair salon | 15–20% | On pre-discount total |
| Pizza delivery | 10–15% or $3–5 minimum | Higher in bad weather |
General Household Budget Ratios (50/30/20 Rule)
| Category | % of Net Income | Examples |
|---|---|---|
| Needs | 50% | Rent, groceries, utilities, insurance |
| Wants | 30% | Dining out, entertainment, hobbies |
| Savings / Debt | 20% | Emergency fund, retirement, extra payments |
Common Measurement Conversions for Everyday Use
| Quantity | US / Imperial | Metric Equivalent |
|---|---|---|
| 1 cup | 8 fl oz | 237 mL |
| 1 pint | 16 fl oz | 473 mL |
| 1 quart | 32 fl oz | 946 mL |
| 1 gallon | 128 fl oz | 3.785 L |
| 1 lb | 16 oz | 453.6 g |
| 1 ft | 12 in | 30.48 cm |