Generator Fuel Consumption Calculator

How much fuel does a generator use per hour?

A generator's fuel use per hour depends on its rated output in kW (kVA × 0.8 power factor for most sets), how much load you actually put on it, and its specific fuel consumption — how many litres it burns per kWh of electricity it delivers. Diesel generators typically use about 0.27 litres per kWh at full load, rising to roughly 0.35 L/kWh at light (25%) load, because engines run less efficiently when they are not working hard — so a lightly loaded generator burns less fuel per hour but more fuel per unit of electricity produced.

For Nigerian households and small businesses, that means a 10 kVA diesel generator run at a typical 50% load burns around 1.16 litres per hour — about 9.25 litres over an 8-hour NEPA outage, or roughly ₦13,900 per day at ₦1,500/litre diesel. This calculator lets you set your own fuel price, load level and hours to get a Naira figure that matches your own generator and outage pattern, rather than a generic global average.

How do I calculate generator fuel consumption and cost?

Multiply the generator's rated output in kW by the load percentage to get delivered kW, then multiply by a fuel-use rate of about 0.27–0.35 litres per kWh (higher at lower loads). Example: a 10 kVA generator (8 kW at 0.8 power factor) run at 50% load delivers 4 kW, so it burns roughly 4 × 0.289 ≈ 1.16 litres of diesel per hour.

Steps to estimate fuel use and Naira cost

1. Convert generator size to kW: kVA × 0.8, the standard power factor most gensets are rated at (skip this step if your generator is already rated in kW).
2. Multiply rated kW by the load percentage you actually run at — most household and SME loads sit at 25-75% of rated capacity, rarely a full 100%.
3. Multiply delivered kW by the litres-per-kWh rate for that load level: 0.268 at 100% load, 0.271 at 75%, 0.289 at 50%, 0.347 at 25% (diesel).
4. Multiply litres per hour by the hours you run the generator each day to get litres per day.
5. Multiply litres per day by your fuel price per litre for cost per day, then by 30 for a monthly estimate — or divide your tank size by litres per hour for full-tank runtime.

Formula

• Rated kW = the generator's continuous output in kilowatts; if your nameplate shows kVA, multiply by 0.8 (the typical power factor)
• Load % = the share of rated output actually drawn — check the appliances plugged in, not the generator's maximum capacity
• SFC = specific fuel consumption in litres per kWh delivered; it is not constant — it rises as load falls because the engine idles a larger share of its work

Quick fuel-use answers for common generator sizes

How much fuel does a 10kVA generator use per hour?

At a typical 50% load, a 10 kVA diesel generator (about 8 kW at 0.8 power factor) uses roughly 1.16 litres per hour. At full (100%) load it rises to about 2.14 L/h; at a light 25% load it drops to about 0.69 L/h — running lightly loaded burns less fuel per hour but more fuel per kWh delivered.

How much diesel does a 5kVA generator use in a day?

Run for 8 hours a day at 50% load, a 5 kVA diesel generator burns about 4.62 litres — roughly 0.58 litres per hour × 8 hours.

How much fuel does a 7.5kVA generator use per hour at 75% load?

About 1.22 litres per hour — 7.5 kVA × 0.8 power factor = 6 kW rated, 75% of that is 4.5 kW delivered, and diesel engines run at about 0.271 L/kWh at 75% load.

What does it cost to run a 15kVA generator for a month?

At 50% load, 8 hours a day and ₦1,500/litre diesel, a 15 kVA generator burns about 13.87 litres a day — around ₦20,800 a day, or roughly ₦624,200 over 30 days. Enter your own price and hours for an exact figure.

Is a generator more fuel-efficient at 100% load or 50% load?

Per kWh of electricity produced, yes — 100% load is more efficient (about 0.268 L/kWh) than 50% load (about 0.289 L/kWh). But per hour, 100% load still burns far more total fuel because it is delivering twice the power.

How big a fuel tank do I need for a 10kVA generator to run 12 hours?

At 50% load, a 10 kVA generator uses about 1.16 L/h, so 12 hours needs roughly 13.9 litres of diesel — plus a margin, since tanks are rarely run down to empty.

Example diesel fuel use by generator size (50% load, 8 hours/day)

Frequently asked questions

Why does higher load mean more fuel per hour but less fuel per kWh?

A generator engine has fixed losses (friction, cooling, idling) that don't scale down much with load, so at low load those losses are a bigger share of total fuel burned per unit of electricity. At high load the engine works closer to its efficient design point, so litres per kWh drop even though total litres per hour rise because it's delivering far more power.

Is diesel or petrol cheaper to run per kWh in Nigeria?

Diesel generators are generally more fuel-efficient per kWh than small petrol generators, especially fixed-speed carbureted models common in Nigeria, but diesel gensets typically cost more upfront and diesel (AGO) and petrol (PMS) pump prices move independently — compare your local diesel and petrol prices per litre against each engine's efficiency, not price per litre alone.

How accurate is this calculator for my exact generator model?

The diesel model averages published specification data from three Caterpillar industrial diesel generator models (275 ekW to 1600 ekW); real consumption varies by brand, engine age, maintenance and altitude. For an exact figure, check your generator's own spec plate, manual, or manufacturer datasheet.

Why are the petrol (PMS) figures shown as a range instead of one number?

Small petrol generators vary enormously — an efficient inverter generator can use under half the fuel of a common fixed-speed carbureted unit at the same load, and few manufacturers publish full load-based fuel tables for small units the way industrial diesel makers do. The range here is anchored to one verified manufacturer figure (Honda EU22i, 0.45 L/h) at the efficient end and typical small fixed-speed Nigerian generators at the higher end.

Does the generator's age or altitude change fuel consumption?

Yes. Older engines, dirty air filters, worn injectors and poor maintenance all increase fuel use above the manufacturer's rated figures. Running at high altitude or high ambient temperature can also reduce efficiency. Treat this calculator's output as a planning estimate, not a guarantee.

This diesel model averages published fuel-consumption tables from three Caterpillar industrial generator sets (C13 350 ekW, 3412C 700 ekW, 3516 1600 ekW) and applies the same litres-per-kWh rate across all generator sizes as an industry-standard approximation — actual consumption varies by brand, engine age, maintenance, ambient temperature and altitude. Petrol (PMS) figures are wide estimate ranges anchored to one manufacturer spec sheet, not model-specific data, because small petrol generators rarely publish full load-based fuel tables. Always check your own generator's spec plate or manual, and treat results here as planning estimates rather than exact readings.

Sources: Caterpillar C13 350 ekW diesel generator set — spec sheet SS-8255355-18489720-000, Caterpillar 3412C 700 ekW diesel generator set — spec sheet SS-7155583-18321546-002, Caterpillar 3516 1600 ekW diesel generator set — spec sheet SS-9599243-1000006026-035, Honda EU22i 2.2 kVA petrol inverter generator — technical data sheet