Generator Fuel Cost Calculator

What this calculator does

A generator is one of those costs that hides in plain sight. Nobody budgets ₦180,000 a month for electricity, but plenty of Nigerian households spend that on fuel without ever adding it up, because it leaves in two thousand naira increments at the filling station rather than as a single bill.

This calculator adds it up. Enter how much fuel your generator uses per hour, what you pay per litre, how many hours a day you run it and how many days a month, plus any servicing costs, and it returns the daily, monthly and yearly total. Add the useful power output and it also calculates your effective cost per unit of electricity, which is the figure that lets you compare generator power against the grid honestly.

That comparison is usually sobering. Self generated power typically costs several times what the same unit costs from the distribution company, and seeing the gap in naira per unit tends to change how people think about inverters, solar and simply running the generator fewer hours.

How the calculation works

The fuel side is straightforward. Litres per hour multiplied by hours per day gives daily consumption. Multiply by days per month and by the pump price for the monthly fuel bill, then add servicing, oil changes and repairs, which are real recurring costs that people routinely leave out.

The cost per unit calculation is where the tool earns its keep. Multiply your useful power output in kilowatts by hours run and days run, and you have the kilowatt hours the generator actually produced. Divide the total monthly cost by that figure and you get your true cost per unit.

Useful output is not the same as the nameplate rating. A generator sold as 2.5 kVA delivers roughly 2 kW of usable power, because kVA to kW conversion carries a power factor of around 0.8. And most people run generators well below their maximum load, which makes the real cost per unit produced even higher than the calculation suggests.

The formula

Litres per day = Litres per hour × Hours run per day

Monthly fuel cost = Litres per day × Days per month × Price per litre

Total monthly cost = Monthly fuel cost + Servicing and maintenance

Units produced per month (kWh) = Useful output in kW × Hours per day × Days per month

Effective cost per unit = Total monthly cost ÷ Units produced

kVA to kW: multiply the kVA rating by about 0.8

A worked example

A household runs a 2.5 kVA petrol generator that uses 1.2 litres an hour, for six hours a day, thirty days a month, with fuel at ₦950 a litre and about ₦8,000 a month on oil and servicing.

Daily consumption is 7.2 litres, costing ₦6,840. Over thirty days that is 216 litres and ₦205,200 in fuel, plus ₦8,000 servicing, for a total of ₦213,200 a month or nearly ₦2.56 million a year.

The useful output of a 2.5 kVA set is about 2 kW, so six hours a day for thirty days produces 360 units. Dividing ₦213,200 by 360 gives an effective cost of ₦592 per unit. Against a grid tariff of ₦225, that generator power costs more than two and a half times as much. Every hour shifted from the generator back to the grid, or to an inverter charged from the grid, is worth roughly ₦730 a day at these figures.

Things worth knowing

Include servicing in the real cost

Oil changes, filters, plugs, repairs and eventual replacement are all part of what the machine costs you. Fuel alone understates the true figure, sometimes by fifteen per cent or more on an older generator.

Right size the machine

A large generator running a light load burns far more fuel per unit delivered than a smaller one running near capacity. If you are running a 10 kVA set to power a fridge and three lights overnight, you are paying for capacity you are not using.

Compare against an inverter honestly

Run this calculator, then work out what the same units would cost from the grid. If the gap is large, the payback period on an inverter and battery bank becomes the real question. Divide the system cost by the monthly saving to see how many months it takes to break even.

Never run it indoors

Generator exhaust contains carbon monoxide, which is odourless and kills. Nigeria records deaths from this every year. Site the generator outdoors with clear ventilation, well away from windows and doors, with no exception for rain or security concerns.

Common mistakes to avoid

Counting only fuel and ignoring oil changes, servicing and repairs.
Using the kVA rating as though it were kilowatts, which overstates output by about twenty per cent.
Estimating fuel consumption from memory rather than measuring it over a few tanks.
Using an old fuel price when pump prices have moved.
Forgetting that a lightly loaded generator is far less efficient per unit produced.
Assuming a larger generator is always better, when it usually means higher consumption for the same useful output.

Frequently asked questions

How much fuel does a small generator use per hour?

A 2.5 kVA petrol generator typically uses somewhere between 1 and 1.5 litres an hour depending on load. Larger and diesel sets vary widely. The reliable approach is to measure your own: fill the tank, note the level, run it for a known number of hours and see what it took to refill.

Is a generator cheaper than grid electricity?

Almost never per unit. Self generated power in Nigeria commonly costs several times the grid tariff once fuel and servicing are counted. Generators buy you availability rather than cheap power.

How do I convert kVA to kW?

Multiply the kVA figure by about 0.8. A 5 kVA generator delivers roughly 4 kW of usable power, and that is before allowing for the fact that most households run well below capacity.

Would solar or an inverter be cheaper?

Over a long enough period usually yes, but the upfront cost is significant and batteries need replacing every few years. Work out your current monthly generator cost with this tool, then divide the installed cost of the alternative by that monthly figure to see the payback period in months.

Does running a generator at low load save fuel?

It uses less fuel in absolute terms but more fuel per unit of electricity produced, and running a diesel generator persistently at very low load can also cause engine problems. Matching the machine to the load is more efficient than under loading a large one.