Why does fuel consumption depend on load?

A generator burns more fuel as it produces more power, but not linearly, because of fixed running losses. At light load it is inefficient per kilowatt-hour, and near full load it consumes the most per hour. Interpolating between the data-sheet points gives a realistic rate for your actual load.

How is propane handled differently?

Propane is often quoted in gallons of liquid but stored by weight or in pounds. The tool treats your input as gallons of liquid propane and uses the manufacturer's gallons-per-hour figures directly, so enter consumption in the same propane units as your fuel quantity.

What load percentage should I use?

Use your real expected load divided by the generator's rated continuous output. Many standby systems run at 30 to 60 percent of rating, which is more efficient and extends runtime compared with running near full capacity.

Why interpolate instead of using one number?

A single full-load consumption figure badly overstates fuel use at part load and understates runtime. Linear interpolation between the 50 and 100 percent points, or 25 percent if supplied, tracks the data sheet far more closely than a flat rate.

Does this account for altitude or temperature?

No. Consumption rises slightly with cold starts, altitude derating, and ageing engines. Treat the result as a planning estimate and keep a fuel reserve, especially for critical standby use during extended outages.

Generator Fuel Runtime Calculator

How long a generator runs depends on how much fuel you have and how hard it is working. This calculator interpolates the manufacturer’s consumption between known load points and divides your fuel quantity by the resulting hourly rate to estimate total runtime.

How it works

Fuel consumption rises with load, so the tool linearly interpolates between the data-sheet rates at 50 and 100 percent load (or 25 percent when supplied) to find the rate at your operating load, then divides fuel by that rate:

rate(load) = interpolate(consumption table, load %)
Runtime hours = fuel quantity ÷ rate(load)

For loads below 50 percent it extrapolates down toward the 25 percent figure where available, otherwise it holds the 50 percent rate as a floor.

Example

A diesel unit burning 0.6 gal/h at 100 percent and 0.4 gal/h at 50 percent, run at 75 percent, consumes about 0.5 gal/h. A 30-gallon tank then lasts roughly 30 ÷ 0.5 = 60 hours.

Tips

Run standby loads at 30 to 60 percent for the best efficiency and runtime.
Keep a fuel reserve — cold, altitude, and engine age raise consumption.
Use the data sheet’s own units for both fuel quantity and consumption.