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ProService Generator Repairs

Fuel tool

Generator fuel consumption calculator

Estimate how many litres a generator uses per hour at a given load, how much it needs for a run, and what that costs at the fuel price you enter.

Your own manufacturer figures give the best answer. Without them, diesel sets are estimated from a published approximate chart. The fuel consumption guide explains why real use differs.

Free to use · No login · Works on a phone

Fuel
Rating unit
kVA

From the data plate. Use the prime or standby rating the plate shows.

%

How hard the set works, as a share of its rating.

Used to convert kVA to kW. 0.8 is the usual rating basis.

h
R/L

Optional. Enter what you pay per litre. No price is assumed.

Manufacturer fuel figures (optional for diesel, needed for petrol)

The specification sheet or manual often lists litres per hour at several loads. Enter any you have; the calculator interpolates between them and uses them instead of the general diesel chart.

L/h
L/h
L/h
L/h

Or use the run time on a full tank from the manual

L
h
%

The load the manual quotes, e.g. 25 or 100.

How the calculation works

  1. A kVA rating is converted to kW: kW = kVA × power factor.
  2. If you enter manufacturer litres-per-hour figures, the figure at your load is interpolated in a straight line between the two nearest points. A load outside your figures is not guessed.
  3. Without manufacturer figures, a diesel estimate comes from the widely republished Diesel Service & Supply approximate fuel consumption chart. Its 20, 100, 200 and 500 kW rows at quarter, half, three-quarter and full load are converted from US gallons to litres (1 US gallon = 3.785 L). Use per rated kW is interpolated between rows and between load points.
  4. Total litres = litres per hour × hours. Cost = total litres × the price you entered.

The chart rows used, in litres per hour:

Approximate diesel use by generator size and load
Rating25%50%75%100%
20 kW2.33.44.96.1
100 kW9.815.522.028.0
200 kW17.829.141.654.5
500 kW41.670.099.9135.1

Sources: Depco: Estimated diesel fuel consumption chart; Power Gen Enterprises: Approximate diesel fuel consumption chart. The chart describes itself as an approximation.

Worked example

A 100 kW diesel set at half load for 10 hours. The chart gives 4.1 US gallons per hour, which is 15.52 litres per hour, so the run needs about 155 litres. Multiply that by the price you pay per litre for the cost; the calculator does the same with the price you enter. A set with a 125 kVA nameplate at a power factor of 0.8 is also 100 kW, so it gives the same answer.

Limits of the estimate

  • The diesel chart is an approximation across many engines. Your engine’s specification sheet is better.
  • Below 25% load the chart has no figure; the 25% value is shown, so real use should be lower.
  • Ratings below 20 kW or above 500 kW are scaled from the nearest chart row and are rougher still.
  • Petrol sets vary too much for a general chart, so the calculator asks for the manual’s figure or its run time on a full tank.
  • Engine condition, altitude, heat, load swings and fuel quality all change real consumption.
  • No fuel price is assumed. Prices change, so enter what you pay.

Fuel safety

  • Never refuel a generator while it is running or hot. Let it cool first.
  • Store fuel in approved containers, away from the generator, living areas and anything that can ignite it.
  • Clean up spills before starting the engine, and do not smoke near fuel.
  • Run generators outdoors, away from doors, windows and vents. Exhaust contains carbon monoxide, which you cannot see or smell.
  • Stored diesel can collect water and grow microbes. See contaminated diesel for the signs.

Related

Guides and services that go with this tool

Using more fuel than you expected?

ProService Generator Repairs works onsite across Gauteng. Send the generator details on WhatsApp or call to arrange a visit.

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