LoadCairn / Standby power
Generator fuel burn & runtime calculator.
Estimate how fast a diesel generator burns fuel at your load, how long a tank lasts, and how big a tank you need. Use your generator's spec sheet fuel rate when you have it.
Planning estimate only
Fuel burn and runtime
Results update in this browser as you edit the inputs.
Burn rate
21.9 gal/hr
82.9 L/hr
Usable fuel
900 gal
of the entered tank capacity
Tank runtime
41.1 h
41 h 6 min · 1.71 days
Fuel for target runtime
526 gal
Minimum tank: 584 gal
Calculation details
Load fraction = running load ÷ generator rating. Burn rate = rating kW × fuel coefficient in estimate mode; spec-sheet mode uses the entered gal/hr rate.
- Load fraction
- 60.0%
- Fuel coefficient
- 0.0438 gal/hr per rated kW
- Usable fuel
- tank × usable % ÷ 100 = 900 gal
- Target fuel
- burn rate × target hours = 526 gal
Runtime = usable fuel ÷ burn rate = 41.1 h = 41 h 6 min. Minimum tank = target fuel ÷ usable fraction = 584 gal.
Assumptions and limitations
Planning estimate only
Diesel fuel; burn rate taken at a steady load.
Estimate mode uses coefficients fitted to published approximate diesel consumption charts. For generators of 100 kW and up the estimate is typically within about 15% of those charts; for smaller sets it can read up to 25% low.
Below 25% load the 25% coefficient is used, which overstates burn and understates runtime (the safer direction).
No allowance for fuel degradation, temperature, altitude, load steps, or engine-specific efficiency.
Sources
Planning references · not endorsements
- Manufacturer generator spec sheets (fuel consumption at 25/50/75/100% load)
- Approximate diesel fuel consumption charts published by generator suppliers (e.g. Generator Source)
- NFPA 110, Standard for Emergency and Standby Power Systems (EPSS class = minimum runtime without refueling)