Fuel is the biggest running cost of a generator, and it decides how big the tank must be. Here is how much diesel a set uses, and how to work out your own numbers.
The quick rule
A modern diesel generator uses roughly 0.26 litres of diesel per kWh produced at 75% load. Efficiency drops at light load and is slightly worse at full load.
Litres per hour ≈ kW of load × 0.26
So a 200 kVA set (160 kW) running at 75% load (120 kW) burns about 31 litres an hour.
Consumption chart
Typical values for modern diesel sets at 0.8 power factor. Exact figures depend on engine model and site conditions — always check the datasheet for the unit quoted.
| Generator (kVA) | Prime kW | 50% load (L/h) | 75% load (L/h) | 100% load (L/h) |
|---|---|---|---|---|
| 20 | 16 | 2.2 | 3.1 | 4.3 |
| 30 | 24 | 3.4 | 4.7 | 6.5 |
| 50 | 40 | 5.6 | 7.8 | 10.8 |
| 60 | 48 | 6.7 | 9.4 | 13.0 |
| 80 | 64 | 9.0 | 12.5 | 17.3 |
| 100 | 80 | 11.2 | 15.6 | 21.6 |
| 150 | 120 | 16.8 | 23.4 | 32.4 |
| 200 | 160 | 22.4 | 31.2 | 43.2 |
| 250 | 200 | 28.0 | 39.0 | 54.0 |
| 300 | 240 | 33.6 | 46.8 | 64.8 |
| 400 | 320 | 44.8 | 62.4 | 86.4 |
| 500 | 400 | 56.0 | 78.0 | 108.0 |
| 650 | 520 | 72.8 | 101.4 | 140.4 |
| 750 | 600 | 84.0 | 117.0 | 162.0 |
| 1000 | 800 | 112.0 | 156.0 | 216.0 |
| 1250 | 1000 | 140.0 | 195.0 | 270.0 |
| 1500 | 1200 | 168.0 | 234.0 | 324.0 |
| 2000 | 1600 | 224.0 | 312.0 | 432.0 |
Each size has its own page with the full specs — for example the 100 kVA, 500 kVA and 1000 kVA generators.
What makes consumption go up
- light loading — a set at 20% load burns more fuel per kWh and suffers wet stacking
- heat — at 50 °C the radiator fan works harder and output is derated
- dirty air filters and poor maintenance — see our maintenance checklist
- oversizing — a set far bigger than the load wastes fuel every hour it runs
How to size the fuel tank
Tank (litres) = L/h at expected load × hours of autonomy × 1.1
The 10% covers the unusable fuel at the bottom of the tank. Example: a 500 kVA set at 75% load for 24 hours → 78 × 24 × 1.1 ≈ 2,060 litres. Standard base tanks usually give around 8 hours; longer autonomy needs a bigger base tank or an external fuel tank.
Running cost per hour
Multiply the litres per hour by the current diesel price. Over a year, 1–2 litres per hour saved by correct sizing adds up to thousands of litres — which is why getting the size right with our kVA calculator pays for itself.
