A generator fuel consumption calculator converts a set's size and load into the fuel it actually burns, in liters per hour (L/h) or gallons per hour (gal/h). It answers the four questions every operator and buyer asks.
How much fuel does this set use per hour? The calculator returns liters per hour and gallons per hour based on your actual load.
How long will it run on a full tank? Enter your tank size and get the hours directly, or calculate the tank size you need for your autonomy target.
What does it cost to run? The calculator shows cost per hour, per day, per year, and cost per kWh — a figure you can budget around.
Most fuel figures online are single-point estimates. The problem is that a diesel generator burns very different amounts at 25%, 50%, 75%, and 100% load. Our calculator uses the multi-load-point method: it applies the engine's specific fuel consumption at each load level, weights it the way your duty does, and returns a burn rate you can actually budget against.
Most online tools give you one number and call it done. Real sites run at a mix of load points through the day, and burn rates vary dramatically.
The calculator uses SFOC curves: about 210 g/kWh at full load, 215 at 75%, 235 at 50%, and 300 at 25% load — interpolated for your exact load.
Prime sets run continuously. Standby sets run only during outages. The calculator applies the load curve the way your site actually operates.
L/h and gal/h, runtime, tank size for your autonomy target, and cost per hour, day, year, and kWh. One screen replaces a spreadsheet.
Enter your generator size, load, fuel price, and autonomy needs. The calculator returns liters per hour, runtime, required tank size, and operating cost — based on real SFOC curves.
Fill in the fields below. The calculator applies a specific fuel consumption curve (SFOC) based on load level.
The chart below is a practical budgeting reference for modern diesel generator sets. The figures are typical values at each load point, and your specific engine will vary by a few percent depending on its SFOC curve and condition.
| Generator Size | 25% Load (L/h) | 50% Load (L/h) | 75% Load (L/h) | 100% Load (L/h) |
|---|---|---|---|---|
| 10 kW | 0.9 | 1.8 | 2.5 | 3.2 |
| 20 kW | 1.7 | 3.5 | 5.0 | 6.5 |
| 50 kW | 4.3 | 8.8 | 12.5 | 16.2 |
| 100 kW | 8.6 | 17.5 | 25.0 | 32.4 |
| 200 kW | 17.2 | 35.0 | 50.0 | 64.8 |
| 500 kW | 43.0 | 87.5 | 125.0 | 162.0 |
| 1,000 kW | 86.0 | 175.0 | 250.0 | 324.0 |
The standard method used by engine manufacturers and fuel consultants is the specific fuel consumption (SFOC) calculation. The formula is straightforward: L/h = kW (actual load) × SFOC (g/kWh) ÷ diesel density (kg/L) ÷ 1,000.
Use the real power the set produces, not the nameplate rating. At 75% load, a 200 kW set produces 150 kW. This is the number that drives the calculation.
Specific fuel consumption varies by load: 210 g/kWh at full load, 215 at 75%, 235 at 50%, and 300 at 25% — interpolate for your exact load.
Multiply actual load in kW by SFOC. For a 200 kW set at 75%: 150 × 215 = 32,250 g/h (about 32.3 kg/h). Mass flow is the intermediate step.
Divide mass flow by diesel density (0.84 kg/L default). 32.3 ÷ 0.84 ≈ 38 L/h. This is your fuel consumption in liters per hour at your actual load.
For fast estimates: 100% load ≈ kW ÷ 4.5 L/h; 75% load ≈ kW × 0.75 × 0.34; 50% load ≈ kW × 0.50 × 0.37.
Actual output: 200 × 0.75 = 150 kW.
SFOC at 75%: 215 g/kWh.
Fuel by mass: 150 × 215 = 32,250 g/h ≈ 32.3 kg/h.
Fuel by volume: 32.3 ÷ 0.84 ≈ 38 L/h.
This set burns roughly 38 liters per hour at 75% load. The calculator applies the curve at your actual load, and our engineers confirm the burn for your exact model before you order.
A fuel budget answers three questions: how long the set runs, how big a tank it needs, and what that costs. Here is how each piece works.
Hours = tank capacity (L) ÷ consumption (L/h). A 100 kW set at 75% load burns about 25 L/h, so a standard 200 L day tank gives roughly 8 hours before refueling.
Multiply burn rate by autonomy target, then add a 20% buffer. A 400 kW set at 75% burns 76 L/h — a 48-hour outage needs about 4,400 L of storage with buffer built in.
Prime sets run continuously and budget fuel at their load curve across the day. Standby sets run only during outages — fuel budget is autonomy hours times burn rate.
Multiply liters per hour by fuel price. At $0.85/L, a 100 kW set burning 25 L/h costs about $21 per hour in fuel.
Divide L/h by kW produced to get L/kWh, then multiply by fuel price. At 0.26 L/kWh and $0.85/L, diesel power costs about $0.22 per kWh before maintenance.
Standby installs often live with a day tank. Prime installs and high-autonomy sites need a fuel farm. We build both packages, including external fuel systems.
Our engineers see these five habits cut fuel bills on nearly every job site that adopts them. Each one is a proven practice, not a theory.
A set running at 70–80% of rating sits in its efficiency band. Oversized sets burn more per kWh and wet-stack. Use our generator sizing calculator to get the size right first.
This is the cheapest operating zone for a diesel engine. Avoid sustained running below 30–40% load where specific fuel consumption climbs sharply.
Air filters, fuel filters, injectors, and coolant keep SFOC low. A tired engine adds up to 15% to your fuel bill — maintenance pays for itself.
Water and contamination cost real money per kWh. Maintain your tanks and filter at the day tank. Clean fuel is the cheapest fuel.
Altitude and heat derate output and raise fuel per useful kWh. Correct your figures with the generator altitude derating calculator before you budget.
Not sure your burn rate is right? Our engineers will review your set, load profile, and site and confirm the fuel figures before you spend anything. Ask our engineers.
Our engineers will review your load profile, confirm the fuel consumption figures, and deliver a factory-direct price — no obligation, no hidden fees. Every quote includes the generator, day tank, and soundproofed enclosure for a complete fuel-efficient solution.
A: A modern set burns about 0.25 to 0.35 liters per kWh it produces. A 100 kW set at 75% load burns about 25 L/h, and a 500 kW set about 125 L/h. Your exact figure depends on load, engine condition, and site.
A: Multiply your actual load in kW by the engine’s specific fuel consumption in g/kWh, then divide by diesel density in kg/L and by 1,000. A 200 kW set at 75% load works out to about 38 L/h.
A: Divide tank capacity by your burn rate. A 100 kW set burning 25 L/h runs about 8 hours on a 200 L tank. A standby set with a bulk tank can run for days.
A: Multiply your burn rate by your autonomy hours, then add a 20% buffer. A site burning 76 L/h that must survive 48 hours needs about 4,400 L of storage.
A: Multiply liters per hour by your fuel price. A 100 kW set burning 25 L/h at 0.85/Lcostsabout0.85/Lcostsabout21 per hour in fuel, roughly $0.22 per kWh.
A: Yes, in liters per useful kWh. Thin air derates engine output, so the set burns similar fuel for less delivered power. Correct your figures with our generator altitude derating calculator.
A: Around 70 to 80% of rated load, where specific fuel consumption is lowest. Running below 30 to 40% load is the most expensive way to operate a diesel set.
A: Usually, yes. Diesel carries more energy per liter and larger diesel sets run at lower specific consumption, so diesel wins on cost per kWh and on runtime for sustained loads.
