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Power & battery

How long will my fuel last, or how far can I drive?

Estimate generator runtime or remaining vehicle range from current fuel, hourly consumption or recent economy, reserve fuel, and a safety margin.

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Formula version 1.0.0 · Last reviewed 2026-09-13

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Calculator inputs and results

Generator fuel runtimeUse current fuel and hourly consumption verified at a similar load to estimate continuous runtime.

Example inputs

Enter fuel actually remaining and a consumption or economy figure close to the planned conditions, not rated tank size.

Current fuel, reserve, and hourly consumption use the same selected unit.
L/h
Use a manufacturer table or measurement at a load close to your plan.
Fuel reserve and variation allowance
L
Fuel you want left after arrival or planned generator operation.
%
Allowance for hourly consumption changing with generator load.

Ready when you are

Check your inputs, then calculate

Check fuel and consumption or economy, then calculate a planning result and range.

Formula and assumptions

For a generator, use consumption measured at a similar load. For a vehicle, use recent economy from similar driving. The result never means that emptying the fuel supply is safe.

Generator runtime = (current fuel − reserve) ÷ hourly consumption. Vehicle mode normalizes fuel and economy to liters and km/L, removes reserve fuel, and then applies another safety margin for a practical range.

Why the result can vary

Generator load, condition, temperature, fuel quality, and vehicle traffic, speed, grade, climate control, gauge error, and detours change the result.

Example

Prepare for an outage or the next fuel stop

Inputs: Generator: 20L, 2L reserve, 1.5L/h; or vehicle: 12L, 14km/L, 3L reserve

Outcome: The generator shows about 12 hours, while vehicle mode reports distance after reserve and a further safety allowance.

Cautions

  • Never operate a generator in an enclosed space; follow manufacturer exhaust, fire, and refueling guidance.
  • Do not plan to empty a vehicle fuel supply; dashboard warnings and road conditions take priority.
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Frequently asked questions

How many hours will 20 liters run a generator?

At 1.5L/h with 2L protected as reserve, the estimate is about 12 hours. Use a manufacturer load table or measurement rather than inferring consumption from rated kW alone.

How far can I drive on the fuel left in my car?

Remaining fuel times recent average economy is the theoretical distance. The calculator removes reserve and a safety margin, but traffic, detours, and gauge error still change real range.

Can I enter L/100km or MPG?

Yes. L/100km, km/L, and US MPG are normalized internally, and the displayed distance follows the selected economy format in kilometers or miles.

Generator runtime and vehicle fuel range calculator guide

Calculate a generator's operating hours or a vehicle's driving range from remaining fuel, with a separate allowance for reserve fuel.

  • Use a generator's hourly consumption at your operating load, or fuel economy observed in your vehicle's actual driving.
  • Compare theoretical hours or distance with the practical result after reserve fuel and any extra safety margin.

Guide updated