Genset diesel consumption per hour: litres by kVA and load

A diesel genset running at three-quarters of its rating burns roughly 0.17 to 0.19 litre of diesel per hour for every kVA. So a 62.5 kVA set at 75% load uses about 11 litres an hour, and a 125 kVA set about 21 litres. The exact figure is on the maker's spec sheet, and it changes a lot with load. Here is what the published sheets say and how to turn them into a monthly bill.

How much diesel does a genset use per hour?

Mahindra Powerol publishes fuel use at 75% and 100% load for each of its diesel sets. These are prime ratings, the rating for long hours of running.

Genset (prime)	Rated kW	Litres/hour at 75% load	Litres/hour at full load
25 kVA	20	4.7	6.2
40 kVA	32	7.3	9.9
62.5 kVA	50	11.3	15.3
125 kVA	100	21.4	28.0
200 kVA	160	33.3	40.8

The sheets add two notes worth reading. The figures assume diesel with a specific gravity of 0.845 (high speed diesel to IS 1460:2005), and they carry a tolerance of +5%. So a set that burns a little more than the chart is still within the maker's figure. The sheets also say the numbers are at standard operating conditions; a hot site or a dirty air filter pushes consumption up.

Other makers publish similar charts. Ask the dealer for the fuel chart of the exact model, because one kVA rating can be sold with more than one engine.

Does a half-loaded genset save diesel?

It saves litres per hour, but not as much as people expect. A Cummins data sheet for its C150 D5 set (136 kVA prime, 109 kW, 6BTAA5.9-G6 engine) gives fuel use at four loads:

Load	Power delivered	Litres/hour	Units (kWh) per litre
1/4	27 kW	12.0	2.3
1/2	55 kW	16.0	3.4
3/4	82 kW	25.0	3.3
Full	109 kW	31.2	3.5

At a quarter load the set delivers a quarter of the power but still burns more than a third of its full-load fuel. Each litre gives about 2.3 units of electricity instead of about 3.3 to 3.5. That is why an oversized genset costs more to run, as our guide on what size genset you need explains. Long hours at very light load also cause wet stacking, where unburnt fuel builds up in the exhaust.

The last column is simple arithmetic: power delivered divided by litres per hour. You can do the same with any maker's chart.

Is a bigger genset more efficient?

Slightly. Working out units per litre from the Mahindra Powerol table at 75% load:

Genset	Units (kWh) per litre at 75% load
25 kVA	3.2
40 kVA	3.3
62.5 kVA	3.3
125 kVA	3.5
200 kVA	3.6

A 200 kVA set gets about 12% more electricity out of each litre than a 25 kVA set. But that only holds if the big set is properly loaded. A 200 kVA set running a 20 kW load is at about 12% of its rating, well below the quarter load in the Cummins table, and wastes far more than it gains.

Worked example: a monthly diesel bill

A small factory runs a 62.5 kVA genset at about 75% load (around 37.5 kW) for 4 hours a day during power cuts, 26 days a month.

• Fuel per hour, from the chart: 11.3 litres
• Fuel per day: 11.3 × 4 = 45.2 litres
• Fuel per month: 45.2 × 26 = about 1,175 litres

At an illustrative ₹90 a litre (check today's price at your local pump), that is about ₹1.06 lakh a month in diesel alone.

Cost per unit of electricity: ₹90 ÷ 3.3 units per litre = about ₹27 per kWh. If the same set ran at a quarter load, at the Cummins sheet's 2.3 units per litre, each unit would cost about ₹39.

Add engine oil, filters and service visits on top. Mahindra Powerol's sheets put lube oil consumption at about 0.15% of fuel consumption for its 30 and 40 kVA sets; the bigger cost is usually the periodic service.

How to check a dealer's fuel claim

1. Ask for the maker's printed spec sheet, not a figure on a quotation.
2. Check whether the figure is at 75% or 100% load, and on the prime or standby rating.
3. Divide the rated kW at that load by the litres per hour. If the answer is well above 4 units per litre, question it.
4. Check the tolerance note. Most sheets allow a few percent either way.
5. For your own set, log the hour meter and the litres filled for a month. Litres divided by hours gives your real figure.

Who makes them

Gensets in India are sold by several makers, including Cummins India, Kirloskar Oil Engines, Greaves Cotton and Mahindra Powerol. Cummins India's quarterly results are on its company page, and you can set the listed engine makers side by side on the compare page.

Sources: Mahindra Powerol genset spec pages for 20–25 kVA, 30–40 kVA, 50–62.5 kVA, 75–125 kVA and 160–200 kVA (mahindrapowerol.com, read 23 Oct 2026); Cummins Power Generation, generator set data sheet C150 D5, 50 Hz diesel (spec sheet SS28-CPGK). Units per litre and the worked example are our arithmetic from these sheets; the ₹90 diesel price is illustrative, not a quoted price.