# How many units should a diesel generator produce per litre, and how do I check mine?

Canonical: https://senseible.earth/answers/diesel-generator-specific-fuel-consumption

A well-loaded diesel generator typically gives about 3 to 3.5 kWh per litre, an estimate based on engine data of roughly 240 to 280 g of diesel per kWh. Check yours by dividing the DG energy meter kWh by the litres used over the same period, and compare with the maker's curve at that load.

## How to run the check

1. Fill the tank to a marked level, or note the flow meter reading, and note the DG energy meter kWh.
2. Run the set for at least a few hours at a steady load you record in kW or percent of rating.
3. Refill to the same mark and note the litres added, and read the kWh again.
4. kWh per litre = kWh generated / litres used. For a monthly figure, use the month's fuel slips and the month's meter readings.
5. Repeat at two or three load levels to see your own curve.

## Converting between kWh per litre and g/kWh

Engine data sheets give specific fuel consumption in grams per kWh. With diesel at about 835 g per litre, a typical density, kWh per litre = 835 / SFC. So 250 g/kWh is about 3.3 kWh per litre and 300 g/kWh is about 2.8.

Ratings are in kVA. Real power in kW is kVA times the power factor, usually taken as 0.8, so a 250 kVA set is about 200 kW.

## Why your figure may be low

- Light load. Engines burn more fuel per kWh at low load; a set running at 25 to 30 percent of rating can lose a large share of its efficiency. The BEE energy auditor guide recommends keeping DG sets well loaded.
- Several sets running together where one would do.
- Dirty air filters, worn injectors or poor fuel.
- Fuel losses: leaks, pilferage or tank readings that do not match purchase slips.
- Long idle running before and after outages.

## What CPCB IV+ does and does not tell you

CPCB IV+ sets exhaust limits for new gensets: NOx, hydrocarbons, carbon monoxide and particulates. It is not an efficiency standard, so a compliant set can still give poor kWh per litre if it is badly loaded. CO2 depends only on the litres burnt.

## Worked example: one month for a factory DG set

- Diesel from fuel slips: 1,200 litres
- DG energy meter: 3,600 kWh
- kWh per litre = 3,600 / 1,200 = 3.0
- Scope 1 = 1,200 x 2.68 = 3,216 kg CO2
- Per unit generated = 3,216 / 3,600 = 0.893 kg CO2 per kWh, against 0.710 for the grid
- At 3.5 kWh per litre the same 3,600 kWh needs 1,028.6 litres, saving 171.4 litres and about 459 kg CO2

2.68 kg CO2 per litre is the IPCC 2006 default for diesel used by Senseible. The 3 to 3.5 kWh per litre range is an estimate; your OEM curve is the reference.

## What Senseible does here

Senseible reads litres from your fuel slips and diesel invoices and gives the Scope 1 figure at 2.68 kg CO2 per litre. The DG energy meter reading comes from your log book, or from a meter feed set up with the Senseible team for your site, which is not self-serve.

- [Diesel generator cost per kWh](https://senseible.earth/answers/diesel-generator-cost-per-kwh)
- [Diesel emission factor](https://senseible.earth/emission-factors/diesel)
- [Is a diesel generator Scope 1 or Scope 2?](https://senseible.earth/answers/diesel-generator-scope-1-or-scope-2)

Sources: [BEE Energy Auditor Guide Book 3, Energy efficiency in electrical utilities, chapter on DG power generating systems](https://beeindia.gov.in), [CPCB, emission norms for diesel gensets (CPCB IV+)](https://cpcb.nic.in), [IPCC 2006 Guidelines, Volume 2: Energy](https://www.ipcc-nggip.iges.or.jp/public/2006gl/vol2.html)

Last reviewed 2026-10-16.