A 20 kW Perkins generator burns about 4.3 litres of diesel per hour at 75% load. A 100 kW at full load burns about 28 litres per hour.
The table: litres per hour by output
| Model | Fuel use (spec sheet) | Tank, enclosed model |
|---|---|---|
| Perkins 15 kW | about 3.3 L/h at 75% load | 50 L |
| Perkins 20 kW | about 4.3 L/h at 75% load | 400 L |
| Perkins 30 kW | about 6.3 L/h at 75% load | 400 L |
| Perkins 40 kW | about 9 L/h at 75% load | 400 L |
| Kubota 40 kW | about 12 L/h at full load (3.18 US gal/h) | open model: 200 L |
| Perkins 50 kW | about 11 L/h at 75% load | 400 L |
| Perkins 60 kW | about 13 L/h at 75% load | 400 L |
| Perkins 80 kW | about 21 L/h at full load | 600 L |
| Perkins 100 kW | about 28 L/h at full load | 600 L |
| Perkins 150 kW | about 38 L/h at full load | 600 L |
Note: the 15 to 60 kW models are rated at 75% load, the 80 to 150 kW models at full load. Compare figures taken at the same load.
Fuel use follows the load, not the size of the machine
A generator does not always burn the same amount of diesel: it burns according to what you connect to it. A 60 kW running 20 kW of equipment uses far less than its 13 L/h at 75%. On the other hand, an undersized machine pushed to its limit burns at its maximum all the time.
That is why choosing the right output matters as much as the price: start with a list of your actual loads. Our guide How to choose a generator’s output explains the method.
Working out run time on a full tank
The math is simple: tank (L) ÷ fuel use (L/h) = hours of operation.
- Perkins 60 kW, 400 L tank, at 75% load: 400 ÷ 13 ≈ 30 hours.
- Perkins 100 kW, 600 L tank, at full load: 600 ÷ 28 ≈ 21 hours.
This is an estimate, not a guarantee: actual load, cold weather and the machine’s condition change the result. For an outage lasting several days, plan for refuelling. For an off-grid site, count the fuel used each day.
Fuel cost
Multiply the litres per hour by the price of diesel in your area. For a farm or a camp that runs every day, do the math over a week: that number often decides the right output.
Keep the tank full
A half-empty tank builds up condensation: water gets into the diesel, and bacteria can grow in it. Refill after each run, but not to the brim, because diesel expands as it warms up. Our standby generator maintenance guide covers the other checks.
Built to run for long hours
Our Perkins and Kubota generators are designed for heavy-duty use, 24 hours a day. Each one is load-bank tested for 2 hours, from 10% to 110%, then adjusted and ready to use. Warranty: 1 year or 1,500 hours.
Frequently asked questions
How many litres per hour does a 20 kW diesel generator use?
About 4.3 L/h at 75% load, according to the spec sheet of our Perkins 20 kW.
How long does a full tank of diesel last?
Divide the tank capacity by the fuel use. A Perkins 60 kW (400 L) at 75% load runs about 30 hours. Actual run time depends on the load.
Does a generator use less fuel at low load?
Yes. In litres per hour, fuel use drops as the load drops. Spec-sheet figures are given at 75% or 100% load.
Diesel or propane: which uses less?
See our comparison standby generator: diesel or propane.
Also read: Which diesel generator for your use? · Diesel generators for sale in Quebec · Standby or prime power?