HP to GPH Calculator: Fuel Flow, Cost and Run Time

Calculate fuel flow in GPH from engine horsepower using BSFC, fuel density and load factor, plus fuel cost per hour and run time on your tank.

What do you want to solve for?

Required: engine power.

Fuel type

Sets typical BSFC and fuel density. You can edit both under Advanced.

Engine power (required)

Load factor (percent of that power in use)

Use 100 for wide open throttle, or about 70 to 80 for a normal cruise.

Advanced: BSFC and fuel density

Optional: fuel cost and run time on a tank

Hp To Gph Formula

GPH = (HP \times BSFC \times LF) / (ρ fuel)

Variables:

GPH is the fuel flow rate in US gallons per hour.
HP is the brake/shaft horsepower (hp).
BSFC is brake specific fuel consumption in lb/(hp·hr).
LF is load factor (fraction from 0 to 1; e.g., 100% load = 1.0).
ρ_fuel is fuel density in lb/US gal.

There is no single universal conversion from horsepower to gallons per hour. However, you can estimate fuel flow from horsepower using BSFC, fuel density, and the operating load factor with the formula above.

Horsepower to Fuel Flow Conversion Table (US gallons per hour, estimate)
Horsepower (hp)	Fuel Flow (US GPH)
1/16	0.0051
⅛	0.0101
1/6	0.0135
¼	0.0203
⅓	0.0270
⅜	0.0304
½	0.0405
⅝	0.0506
⅔	0.0540
¾	0.0608
⅞	0.0709
1	0.0810
1¼	0.1013
1⅓	0.1080
1½	0.1216
1¾	0.1418
2	0.1621
2½	0.2026
3	0.2431
4	0.3241
Estimates assume gasoline defaults used by this page (BSFC = 0.50 lb/(hp·hr), fuel density = 6.17 lb/US gal) at 100% load (LF = 1.0). This implies 1 hp ≈ 0.081 US GPH*.

How to Calculate Hp To Gph?

The following steps outline how to estimate fuel flow (GPH) from horsepower (or horsepower from fuel flow) using BSFC, fuel density, and load factor.

First, determine the horsepower (hp) or the fuel flow rate (GPH).
Next, choose or determine the BSFC (lb/(hp·hr)), fuel density (lb/US gal), and load factor (0 to 1).
Then use the formula: GPH = (HP × BSFC × LF) ÷ ρ_fuel (or rearrange to solve for HP).
After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem :

Use the following variables as an example problem to test your knowledge.

horsepower (hp) = 456 (assume gasoline BSFC = 0.50 lb/(hp·hr), fuel density = 6.17 lb/US gal, and load factor = 100%). Estimated fuel flow: GPH = (456 × 0.50 × 1.0) ÷ 6.17 ≈ 36.95 US GPH.

FAQs

What does GPH stand for in the context of this calculator?
GPH stands for gallons per hour, a fuel flow rate. In this calculator it represents US gallons of fuel per hour (unless you select LPH or IGPH).

Why is it important to know the GPH for a given horsepower?
An estimated GPH helps with planning fuel needs and operating costs. Keep in mind horsepower alone does not determine GPH—fuel flow depends on engine efficiency (BSFC), fuel type, and load.

Can the HP to GPH formula be used for any type of engine?
The relationship here is an engineering estimate based on BSFC and fuel density, and it can be used broadly if you choose appropriate BSFC/density values for your engine and fuel. Manufacturer data or measurements are best for precise results.

Is there a way to improve the fuel efficiency reflected by the GPH value?
Yes. Improving efficiency typically means lowering BSFC for the same power output (or reducing required power): good maintenance, correct tuning, avoiding unnecessary load, and operating in an efficient RPM/load range can all reduce fuel use.