Fuel consumption is expressed in litres per hour (L/h) or gallons per hour (gal/h). It varies with generator size, electrical load, engine efficiency, and site conditions. This page gives you the reference data and calculation methods you need for accurate project planning.
The volume of diesel fuel consumed per hour of operation at a given load level.
Imperial or US gallons per hour — a common unit for North American generator specifications.
Fuel consumption per kilowatt-hour (L/kWh) is the most useful measure for comparing efficiency across different generator sizes.
Fuel is the largest operating expense for most diesel generator installations. Understanding consumption helps you budget accurately, size the fuel tank correctly, compare generator options, and avoid costly surprises during long-duration operation.
Larger sets consume more fuel at full load, but the load factor — the percentage of rated capacity being used — has a direct impact on L/h.
Modern engines with low specific fuel consumption (SFOC) — around 200–215 g/kWh — deliver better fuel economy than older designs.
Altitude, ambient temperature, fuel quality and maintenance all affect real-world consumption, often beyond nameplate estimates.
Approximate fuel consumption in litres per hour for common generator sizes at four load levels. Figures assume a modern diesel engine with SFOC of 200–215 g/kWh and standard diesel density of 0.84–0.85 kg/L.
| Generator Size (kW) | 25% Load | 50% Load | 75% Load | 100% Load |
|---|---|---|---|---|
| 10 kW | 0.9 | 1.8 | 2.5 | 3.2 |
| 20 kW | 1.7 | 3.5 | 5.0 | 6.5 |
| 30 kW | 2.6 | 5.3 | 7.5 | 9.7 |
| 50 kW | 4.3 | 8.8 | 12.5 | 16.2 |
| 80 kW | 6.9 | 14.0 | 20.0 | 25.9 |
| 100 kW | 8.6 | 17.5 | 25.0 | 32.4 |
| 150 kW | 12.9 | 26.3 | 37.5 | 48.6 |
| 200 kW | 17.2 | 35.0 | 50.0 | 64.8 |
| 250 kW | 21.5 | 43.8 | 62.5 | 81.0 |
| 300 kW | 25.8 | 52.5 | 75.0 | 97.2 |
| 400 kW | 34.4 | 70.0 | 100.0 | 129.6 |
| 500 kW | 43.0 | 87.5 | 125.0 | 162.0 |
| 600 kW | 51.6 | 105.0 | 150.0 | 194.4 |
| 800 kW | 68.8 | 140.0 | 200.0 | 259.2 |
| 1000 kW | 86.0 | 175.0 | 250.0 | 324.0 |
Note: All values are litres per hour. Actual consumption varies by engine model, age, altitude, temperature, fuel quality and maintenance. Use these figures as a planning reference, not a guaranteed specification.
Three practical methods let you estimate fuel use with increasing accuracy. Use the quick rule for budgeting, the SFOC formula for tighter estimates, or the kVA conversion for generator sets rated in apparent power.
The fastest way to estimate consumption uses rated power, load percentage and a fixed factor.
Fuel (L/h) ≈ kW × load % × 0.25 Example: 200 kW at 75% load → 200 × 0.75 × 0.25 = 37.5 L/hThis rule reflects the typical 0.25 L per kWh produced by a modern diesel set. Works well for budgeting and initial sizing.
Use specific fuel consumption (SFOC) in grams per kilowatt-hour for tighter estimates.
Fuel (L/h) = (kW × SFOC) ÷ (density × 1000) SFOC = 200–215 g/kWh | density = 0.84–0.85 kg/LWorked example: 400 kW at full load with SFOC 210 g/kWh and density 0.85 kg/L → (400 × 210) ÷ (0.85 × 1000) ≈ 98.8 L/h.
Most generators are rated in kVA. Convert to kW before applying either formula using a standard power factor.
kW = kVA × 0.8 Standard power factor for diesel generator setsExample: A 500 kVA set = 400 kW. At 75% load (300 kW), it consumes roughly 75 L/h using the quick rule.
Diesel generators are most efficient between 70% and 85% load. Understanding fuel cost per day and tank sizing helps you plan operating budgets and runtime requirements with confidence.
Peak efficiency occurs between 70% and 85% load, where modern engines achieve roughly 0.25 L per kWh. Below 50% load, consumption per kWh rises sharply because fixed losses remain constant while output falls.
At 25% load, consumption can reach 0.36 L/kWh — about 40% more fuel per unit of power than at full load. Prolonged light loading below 30% also causes wet stacking.Calculate running cost from consumption and local diesel price:
Cost/h = L/h × diesel price Cost/day = cost/h × hours run per dayWorked example: 100 kW at 80% load consumes 20 L/h. At $1.20/L: cost/h = $24.00, cost/day (6 h) = $144.00, cost/kWh = $0.30.
Typical diesel generation costs fall between $0.30 and $0.50 per kWh, depending on fuel price, load and engine efficiency.
For backup or off-grid applications, tank capacity determines runtime between refills.
Tank capacity (L) = L/h × required runtime (h) × 1.15–1.2 15–20% margin covers unusable volume and reserveWorked example: 500 kVA (400 kW) at 75% load consumes 75 L/h. For 48 h backup: 48 × 75 × 1.2 ≈ 4,320 litres minimum.
ShanHua supplies base-frame tanks, containerized systems and external storage for any runtime requirement.
Fuel consumption is one part of total cost of ownership — the generator itself is the other. ShanHua manufactures diesel generator sets from 8 kVA to 4,000 kVA, with engines from Cummins, Perkins, Weichai and Yuchai, built to order for your exact load profile.
A: A 100 kVA generator (80 kW) consumes roughly 10 L/h at 50% load, 15 L/h at 75% load, and about 20 L/h at full load. Exact figures depend on engine brand, age and operating conditions.
A: A modern diesel generator typically consumes 0.25–0.33 L per kWh at its most efficient load range (70–85%). At light loads below 50%, consumption per kWh rises significantly.
A: Diesel generators run most efficiently at 70–85% of rated load. Below 30% load, fuel consumption per kWh can climb 20–30% or more, and prolonged light loading can cause wet stacking.
A: Right-size the generator to your actual load, run it in its efficient 70–85% range, perform regular maintenance (filters, oil, injectors), and avoid prolonged light loading. Selecting a modern engine with low SFOC also improves efficiency.
A: Standby generators operate intermittently during utility failures, while prime-rated sets run continuously under varying loads. Prime power generators are often slightly less fuel-efficient at low loads but are designed for extended operation. Fuel consumption at the same load percentage is similar between ratings, but duty cycle affects total fuel used over time.
