Generator Fuel Consumption Calculator — L/h,…

Fuel-rate, duration and reserve-aware runtime model

Estimate generator fuel use without pretending one generic fuel curve fits every engine. Enter the actual electrical load and the specific fuel consumption (SFC) from the generator data sheet, test record or deliberate planning assumption. The result keeps the assumption visible and converts it into hourly burn, trip fuel, tank runtime and cost.

How to use this calculator

Enter the real average electrical load in kW, not generator nameplate kW unless it actually runs at full load.

Enter SFC in L/kWh from the manufacturer fuel curve at the relevant load when available.

Enter planned operating hours and local fuel price per litre.

Optionally enter tank capacity and a deliberate reserve percentage to estimate usable runtime.

Use the estimate for fuel logistics and budgeting, then compare against measured consumption or the exact generator fuel curve.

Where people use it

•Estimate diesel needed for an outage or planned generator run.
•Convert a manufacturer SFC point into litres/hour and US gallons/hour.
•Estimate usable runtime from a day tank while preserving a fuel reserve.
•Budget hourly, shift and event fuel cost from an actual load forecast.

Example: 40 kW load at 0.28 L/kWh for 8 hours

Fuel rate is 11.2 L/h. An 8-hour run needs 89.6 L, about 23.67 US gal. A 120 L tank with 10% reserve provides 108 L usable fuel and about 9.64 hours at that assumed burn rate.

Use manufacturer or measured fuel data for final planning

•SFC is not universal. Use the exact manufacturer fuel-consumption curve or measured site data at the expected load whenever available.
•Do not calculate fuel from generator nameplate kW when the actual load is lower. Fuel burn follows engine operating point and includes losses.
•A constant entered SFC is a point estimate. Real part-load efficiency is nonlinear, especially at light load; use multiple manufacturer curve points for a duty-cycle study.
•Altitude, ambient temperature, fuel properties, engine condition, auxiliaries and transient loading can change measured consumption.
•Tank runtime assumes the entered reserve is unavailable and does not model unusable heel, piping, day-tank transfer, leak/spill allowance or minimum fuel-return requirements.
•This calculator does not select a generator size, certify emergency runtime, prescribe fuel storage or replace fire/environmental/code requirements.

Frequently asked questions

How do I calculate generator fuel consumption per hour?+

With a known specific fuel consumption, multiply actual electrical load in kW by SFC in L/kWh. For example, 40 kW × 0.28 L/kWh = 11.2 L/h.

Should I use generator rated kW or actual load?+

Use actual average electrical output for this SFC method. Using nameplate rating when the generator is partially loaded overstates the useful-output term and can produce a misleading estimate.

What SFC should I enter?+

Prefer the manufacturer fuel curve or a measured site value at the expected load. A generic L/kWh figure is only a planning assumption because part-load efficiency differs by engine and operating condition.

Why does a lightly loaded generator not use proportionally less fuel?+

Engines have fixed and load-dependent losses, so fuel per kWh commonly worsens at light load. A single constant SFC cannot reproduce the whole part-load curve.

How is tank runtime calculated?+

The calculator first removes the entered reserve from tank capacity, then divides usable litres by the calculated litres per hour.

Does this calculate starting surge fuel?+

No. Short motor-start transients matter primarily for generator electrical sizing and transient response. Fuel planning should use the expected operating duty/load profile or manufacturer data.

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