Genset Fuel Consumption per Hour: Litres by kVA and Load

How much diesel does a genset use per hour?

A diesel genset in the 25 to 500 kVA range uses about 0.26 to 0.33 litres of diesel for every kWh it delivers when it runs between three-quarter and full load. Multiply your load in kW by that figure and you have litres per hour.

Two words need explaining first. kVA is the size printed on the set. kW is the real power your machines use, and on a standard Indian set it is 0.8 times the kVA, so a 125 kVA set is a 100 kW set. Fuel follows kW, the work being done, and not kVA.

The ratio holds across very different sets. The smallest sets are the exception. A 7.5 kVA set needs closer to half a litre for each kWh, because its engine losses are large compared with the little power it makes.

So the short answer is: a set loaded to 60 kW burns roughly 16 to 20 litres an hour, a set loaded to 300 kW burns roughly 80 to 100 litres. The tables below show where those ranges come from.

What do maker data sheets say about litres per hour by kVA?

The Indian maker sheets we found print fuel use at two points, 75% and 100% of the prime rating. Prime rating means the power the set can give for unlimited hours with a varying load, which is how a site set is used. The table below collects the figures from the sheets we downloaded and read in November 2026.

Read the table with three cautions. The Cummins sheets base their figures on diesel with a specific gravity of 0.85 to IS 1460 and allow a tolerance of plus 5%; the Mahindra pages use 0.845 and the same plus 5%. That tolerance means a healthy set can burn up to 5% more than the sheet and still be in specification.

Second, the figures are for the set with its radiator fan running, which is how it works on site. Third, the Mahindra pages carry older engine codes and the two Cummins sheets date from 2018 and 2021, before the CPCB IV+ emission rules for new sets from July 2023. The newer CPCB IV+ brochures and product pages we read from Mahindra Powerol, Cummins India and Kirloskar do not print litres per hour at all, so ask the seller for the sheet of the exact model you are offered.

The pattern is still clear. From 15 kVA upward, a set at full load turns one litre of diesel into a little over 3 kWh, and the biggest sets come closer to 4. Below about 10 kVA the figure gets worse fast.

Does a generator use less fuel at half load?

Yes in litres, no in efficiency. A genset at half load burns noticeably more than half its full-load fuel, so each kWh costs more diesel. The Indian sheets above stop at 75% load, so the part-load picture below comes from Caterpillar’s 50 Hz data sheets, which print fuel at 25%, 50%, 75% and 100% load. They are European Stage IIIA sheets dated 2020 to 2022, not CPCB sets, but the engine behaviour they show is the same.

Take the 400 kVA set. At a quarter of its load it still burns 27.9 litres an hour, which is 32% of its full-load fuel while it makes 25% of the power. Part of the engine’s fuel goes into simply keeping itself turning at its fixed speed, 1,500 rpm on a standard 50 Hz set, and that share stays the same whatever the load.

Figure 1: Diesel needed for each kWh, Caterpillar DE450E3 (400 kVA prime)

Longer bar = more diesel for the same unit of electricity. Figures from the maker’s 50 Hz sheet LEHE1635-01 (05/20), divided by the prime kW at each load.

This is why the Bureau of Energy Efficiency’s guide book on DG sets says engine loading should be kept above 50%, and that the set rating should be only 10 to 20% more than the power the site actually needs. An oversized set idling along at 25% load is the most common way a site wastes diesel.

How do you calculate generator fuel consumption per hour?

Use this four-step method. It needs only your load and the set’s data sheet.

1. Find the real load in kW. Add the running kW of the machines that work together: motors, the welding set, pumps, lights. If you only know amps, the sizing method shows how to read nameplates.
2. Work out the load percentage. Divide your kW by the set’s prime kW. A 60 kW load on a 125 kVA (100 kW) set is 60% load.
3. Pick the litres per kWh for that load from the maker’s sheet, or from the tables above if you have no sheet yet. Around 0.30 suits a mid-size set at 50 to 75% load; use 0.33 to 0.37 below half load.
4. Multiply. Litres per hour = load in kW × litres per kWh. For a shift, multiply again by the hours run.

Worked example (our arithmetic). A building site runs a Schwing Stetter SP 1200 E electric concrete pump, whose motor is rated 45 kW, plus a batching unit, lights and small tools. Over a 10-hour pour the average draw comes to about 60 kW on a 125 kVA set.

• Load: 60 ÷ 100 = 60%.
• Litres per kWh at that load: about 0.29 to 0.31, between the 75% figure on the 125 kVA sheet and the half-load trend in the Caterpillar table.
• Fuel: 60 × 0.29 to 0.31 = about 17 to 19 litres an hour, or roughly 175 to 185 litres for the 10-hour pour.

Now put the same 60 kW on a 250 kVA (200 kW) set because “bigger is safer”. The load falls to 30%, the litres per kWh climbs towards 0.33 to 0.35, and the set burns about 20 to 21 litres an hour for the same work. That is up to about 35 extra litres in one 10-hour shift, around 25 at the middle of both ranges, for no extra concrete. Oversizing has a fuel cost every day the set runs.

The same method gives you running time on a tank: hours = usable litres in the tank ÷ litres per hour. Ask the supplier for the usable tank capacity, since the last few litres sit below the pickup.

How many units does a DG set give per litre of diesel?

Turn the ratio upside down and you get units (kWh) per litre, the figure many site engineers track. At full load the sheets above work out to about 3.2 to 3.6 kWh per litre for a 25 to 125 kVA set and about 3.9 for a 500 kVA set. A 7.5 kVA set gives only about 2.1.

The Bureau of Energy Efficiency DG set chapter lists “specific power generation kWh/liter” as one of the checks in an energy audit of a DG set. Its sample monitoring table, from sets of 200 to 920 kW in real service, records 0.290 to 0.362 litres per kWh. That is about 2.8 to 3.4 units per litre, a little worse than the data sheets, which is normal once a set has run for years with a varying load.

Use the figure as a health check. If a set that used to give 3.2 units per litre now gives 2.7 at the same load, something has changed: a choked air filter, worn injectors, a leak or diesel going missing.

How do you check a genset’s actual fuel use on site?

Data sheets tell you what a set should burn. A simple log tells you what it does burn. You need three readings each day.

• Fuel added. Top the tank to the same mark at the same time every day and write down the litres added. Those litres are what the set used since the last top-up.
• Hours run. Read the hour meter on the control panel at each top-up.
• Units made. Most controllers show kWh. Note it with the hours.

Litres ÷ hours gives litres per hour. kWh ÷ litres gives units per litre, and that one is fairer, because it does not change just because the site was quieter that day. Watch the week’s trend, not a single day.

Machines on a site are logged the same way. The excavator fuel consumption per hour page uses the same top-up method, and a site running both can keep one diesel register for all of them.

What makes a genset burn more diesel than its data sheet?

Most of the gap between the sheet and the site comes from a handful of causes.

Power factor matters less than people think for fuel. A low power factor makes the alternator carry more current and can trip the set before the engine is fully loaded, but the engine burns diesel for the kW, not the kVA.

If your genset is there mainly to run an electric concrete pump, it is worth comparing stationary concrete pumps on their motor rating before you fix the set size, since the pump is usually the biggest single load. Electric machines charged from a set follow the same arithmetic; the charging guide covers site power for them.

What should you ask before you buy or hire a genset?

Fuel is the largest running cost of a site set over its life, so ask for the numbers before you sign.

• The data sheet for the exact model, with fuel at 50%, 75% and 100% of prime load, and the specific gravity and tolerance it assumes.
• Whether the figure includes the radiator fan.
• The prime rating and the standby rating, and which one the price or rent is quoted on.
• The CPCB IV+ type approval for the set; rules and labels are explained in DG set permission on a construction site.
• The usable tank capacity, so you know how often the set needs filling.
• For hired sets, who pays for diesel and how the hours are logged; the generator rental business guide explains how rental firms charge.

For hire, browse machines and site equipment available on rent near your project. For more on sets, types and rules, the genset guide collects every page in this series.