Worked example
A generator consuming 2 L/hr at ₹95/litre costs about ₹760.00 for 8 litres over a 4-hour power cut.
Calculate your generator's fuel cost
Generator Fuel Consumption Calculator
From your genset's own rated consumption
Total fuel cost
₹760.00
8 litres · ₹190.00/hour
Cost per unit vs grid power
Diesel generator, at ₹95/L
≈ ₹29.69/unit
Assumes ~3.2 units of output per litre — a typical planning figure, not a spec-sheet value.
Grid power (TNEB top slab)
₹6.75/unit
Your own state's rate may differ — see our electricity calculators.
A new, well-maintained generator typically runs at 85-90% efficiency; older units, or ones run well below their rated load, can drop to 70% or lower — which pushes the real ₹/unit cost higher still.
Related calculators
Frequently asked questions
Why does this calculator ask for my generator's own consumption rate instead of estimating it from kVA?
Fuel consumption per hour depends heavily on load percentage, engine efficiency and generator design — figures vary widely between models even at the same kVA rating. Rather than guess with a generic multiplier, we use the rate your manufacturer already measured and published for your specific unit, which is far more accurate.
Where do I find my generator's fuel consumption rate?
Check the spec sheet or manual that came with the generator — manufacturers typically publish litres/hour figures at 50%, 75% and 100% load. Use the figure closest to how you actually run it.
Does load level change fuel consumption a lot?
Yes, significantly — a generator running at 50% load typically burns noticeably less fuel per hour than at 100% load, though not exactly half, since some fuel is used just to keep the engine running regardless of output. Use the load-specific figure from your spec sheet closest to your real usage for the most accurate result.
How much more expensive is generator power than grid electricity?
Substantially more — a diesel generator typically works out to somewhere in the ₹18-35/unit range depending on fuel price and genset efficiency, versus roughly ₹5-10/unit for grid power in most states. In Tamil Nadu, for example, TNEB's real top-slab rate is ₹6.75/unit — a generator can easily cost 3-5x that per unit.
How efficient are diesel generators really?
A new, well-maintained generator typically converts diesel to usable electrical output at around 85-90% efficiency; older units, or ones running well below their rated load, can drop to 70% or lower — which is part of why real-world ₹/unit costs vary so much between gensets.
Is it cheaper to run a generator or switch to an inverter/battery backup?
For short, infrequent outages, a battery-based inverter is usually cheaper per outage since it just draws pre-stored grid electricity at your normal tariff rather than burning fuel at generator-level cost per unit. For long or very frequent outages, or high continuous loads, a generator can still make sense — compare using our inverter sizing and backup time calculators.
Does generator age affect running cost?
Yes — engine wear and looser tolerances in an older generator generally reduce fuel efficiency, meaning more litres burned for the same electrical output compared to when it was new. If your generator is several years old, its real consumption rate may now run higher than its original spec-sheet figure.