Generator Fuel Consumption Calculator
Estimate how much diesel a generator burns per hour, the total fuel over a run, and the fuel cost, from the electrical load and a specific fuel consumption figure.
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Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.
How to use this calculator
- Enter the generator load P in kilowatts (kW) — the electrical power being drawn, not the set's nameplate rating.
- Set the specific fuel consumption in litres per kWh (default 0.28 for a mid-loaded diesel) and the number of run hours.
- Optionally enter a fuel price in dollars per litre to get an estimated cost alongside the litres.
How it works
Fuel burn scales with electrical output: rate (L/h) = load P (kW) × specific fuel consumption SFC (L/kWh). Multiplying by the run hours gives the total litres, and multiplying that by the fuel price gives the cost. The 0.28 L/kWh default reflects a diesel set running at a healthy mid-to-high load; lightly loaded sets are less efficient.
Worked example
Worked example. A 40 kW load runs for 8 hours at an SFC of 0.28 L/kWh with diesel at $2.00/L. Rate = 40 × 0.28 = 11.2 L/h; total = 11.2 × 8 = 89.6 L; cost = 89.6 × $2.00 = $179.20.
Common mistakes
- Using the generator's nameplate kVA/kW instead of the actual load it is carrying — fuel burn tracks the real load, not the rating.
- Assuming a fixed L/kWh across all loads; efficiency drops (higher L/kWh) at light load and can cause wet-stacking on diesels.
- Forgetting that ambient temperature, altitude and engine condition shift real consumption away from the data-sheet average.
Frequently asked questions
What specific fuel consumption should I use?
Diesel gensets typically use about 0.25–0.30 L/kWh at moderate-to-high load, so 0.28 is a reasonable default. For an accurate figure, read the fuel-consumption curve on your set's data sheet at the load you expect to run.
Can I use this for petrol or gas generators?
Yes — just enter the appropriate specific fuel consumption for that fuel and unit. The formula (rate = load × SFC) is the same; only the SFC value and the fuel price change.
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