How much diesel does a 5 kVA generator use per hour?

A 5 kVA diesel generator at 0.8 power factor makes about 4 kW at full load. At 50% load (2 kW) it burns roughly 0.7 litres/hour; at 75% load (3 kW) about 0.84 litres/hour. Fuel use scales with the actual load, not the nameplate kVA, so a lightly loaded set uses far less.

How do I calculate generator running cost per hour in Sri Lanka?

Multiply litres burned per hour by the fuel price. Litres/hour = kW load × specific fuel consumption (about 0.28–0.40 L/kWh for diesel). For a 2 kW load at 0.35 L/kWh and Rs 392/L diesel: 2 × 0.35 × 392 = Rs 274/hour. This calculator does every step for you.

Is running a generator cheaper than CEB electricity in Sri Lanka?

Not once you count everything a generator costs, but on fuel alone the gap for a household is smaller than many people expect. A diesel set burns Rs 105.84–137.20 of fuel per kWh between full and half load. A household using more than 180 units a month pays CEB Rs 100 for every unit past 180, so the generator's fuel costs 6% more than those units at full load and 37% more at half load — before engine oil, servicing and the price of the set, which this tool does not count. Below 180 units CEB charges Rs 5–44 a unit, though a generator's output can push a bill past 180 and re-price all of it. Shops and offices on the GP-1 tariff pay Rs 27–36 a unit, so a diesel generator costs them 2.9–5.1 times as much. Pick your tariff and enter your usual monthly units above, and the tool prices the generator's energy on your own bill.

What CEB rate does the generator-vs-grid comparison use?

Not a single rate, because there isn't one. Sri Lanka's electricity tariff is banded: what a unit costs depends on how many units the whole bill has, and crossing 180 units re-prices every unit on a domestic bill. So the tool takes your tariff and the units on your usual monthly bill, prices that bill with and without the generator's monthly energy using this site's electricity bill calculator (the PUCSL tariff effective May 11, 2026), and divides the difference by the generator's kWh. In the 5 kVA worked example, the generator's 240 kWh a month would take a 90-unit domestic bill from Rs 1,840.00 to Rs 23,350.00, Rs 89.63 a unit. For GP-2, industrial or time-of-use connections, choose "My own rate" and type your tariff.

How much fuel does a generator use at 50% load versus full load?

Per hour, a half-loaded set burns roughly half the fuel of a full-loaded one because it is doing half the work. But per kWh it is slightly less efficient: a diesel engine uses about 0.35 L/kWh at 50% load versus 0.27 L/kWh at full load, since idling and friction losses are spread over less output.

How many litres per hour does a 10 kVA diesel generator consume?

At 0.8 power factor a 10 kVA set makes 8 kW at full load. At 75% load (6 kW) it burns about 6 × 0.28 = 1.68 litres/hour; at full load about 8 × 0.27 = 2.16 litres/hour. Enter your own load level and fuel price above for an exact figure.

What power factor and load level should I use?

Most generators are rated at 0.8 power factor, use that unless the nameplate says otherwise. For load level, a standby set powering a home or shop during an outage usually sits at 40–75% of its rating; 100% is rare and hard on the engine. Pick the band closest to your real usage.

Does this include servicing, oil and generator purchase cost?

No. This tool covers fuel running cost only. Engine oil, filters, servicing, hire and the capital cost of the generator are separate. For the purchase-and-import side, use the Generator Import Tax Calculator linked below; this tool answers what it costs to keep running.

Where do the fuel prices come from?

Fuel-price defaults mirror the Ceylon Petroleum Corporation (CPC) retail prices effective October 1, 2026, the same figures used across this site's fuel tools. Every price is editable, so if your pump price differs or a new CPC revision lands, type it in and the results update instantly.

Sri Lanka · Finance

Sri Lanka Generator Running Cost Calculator

See what a diesel or petrol generator actually costs to run, fuel burned per hour, cost per day and month, and the real price per kWh versus CEB grid power. Uses current CPC fuel prices. No signup, no ads, sources cited.

By Induwara Ashinsana· Co-Founder, Ryzera TechnologiesUpdated Sep 25, 2026

Generator running cost

CPC price · Oct 1, 2026

Common sizes

Generator rating

kVA

From the nameplate, apparent power in kVA.

Power factor

kW ÷ kVA. Most gensets are rated at 0.8.

Fuel type

Default price is the latest CPC retail figure.

Fuel price

Rs/L

Editable, override with your pump price.

Load level

Hours per day

Running time on a typical day.

Days per month

Days the genset runs each month.

Your CEB / LECO tariff

Households, the standard residential connection.

Units on your monthly bill

units

From your usual CEB bill, without the generator's hours.

Cost per month

Rs 42,806

Cost per day

Rs 1,646

diesel per hour

0.84 L

109.2 L per month

Cost per kWh

Rs 109.76

Verified two ways ✓

Generator vs CEB grid

Generator (fuel)Rs 109.76/kWh

CEB grid, on your billRs 93.62/kWh

From CEB on the Domestic (D-1) tariff, these 390 kWh a month would take a 90-unit bill to 480 units: Rs 1,840 → Rs 38,350, or Rs 93.62 a unit. That moves the bill into a higher band, which re-prices the units you already use as well, the figure includes it.

Running this generator costs 1.17× as much per kWh as CEB grid power, about Rs 6,296 extra a month for the same energy, on fuel alone.

Breakdown

Metric	Value
Electrical load	3 kW
Fuel consumption	0.84 L/hr
Cost per hour	Rs 329
Cost per day	Rs 1,646
Fuel per month	109.2 L
Energy per month	390 kWh
Cost per month	Rs 42,806

Fuel running cost only. Excludes servicing, oil, hire and capital cost. Effective Rs/kWh = SFC × fuel price and is independent of load hours.

Sources: CEYPETCO retail fuel prices and the Approximate Diesel Generator Fuel Consumption Chart (SFC band). The grid side is priced on the PUCSL tariff by this site's electricity bill calculator. Full citations below the tool.

How it works

A generator's fuel bill comes down to three things: how much power you actually draw, how efficiently the engine turns diesel or petrol into that power, and what the fuel costs. The calculator chains those together in five steps, all shown in the breakdown, and a sixth prices the same energy on your own CEB bill.

Real power.A generator's nameplate is in kVA (apparent power). Real power in kW = kVA × power factor. Most sets are rated at 0.8, so a 10 kVA set makes 8 kW at full load.
Actual load. Standby sets rarely run flat out. kW load = rated kW × load level% , pick 25/50/75/100% to match how hard yours works.
Fuel consumption. litres/hour = kW load × SFC, where SFC (specific fuel consumption, litres per kWh) is read from the standard diesel-genset consumption chart. Diesel sits in a ~0.27–0.40 L/kWh band, about 0.28 at 75% load, rising to 0.4 at 25% load, because a lightly-loaded engine wastes proportionally more fuel on friction and idling. Petrol runs a higher ~0.40–0.55 band.
Cost. cost/hour = litres/hour × fuel price, then × hours/day and × days/month for the daily and monthly totals. Fuel-price defaults are the latest CPC retail figures and are editable.
Per-kWh cost. The effective cost of each unit generated is cost/hour ÷ kW load = SFC × fuel price , notice the load cancels, so Rs/kWh depends only on efficiency and fuel price, not on how many hours you run.
Grid comparison.There is no single CEB rate to divide by: the tariff is banded, and the band depends on the whole month's units. So the tool prices your usual monthly bill twice on this site's electricity bill calculator , as it is, and with the generator's monthly kWh added, and divides the difference by those kWh. grid Rs/kWh = (bill with − bill without) ÷ kWh is what the same energy would cost from CEB, band changes and fixed charges included, and the generator's Rs/kWh divided by it is the "× the grid" multiplier.

The tool derives Rs/kWh two ways, cost ÷ energy, and the direct SFC × price identity, and flags them as verified when they agree, so you can trust the number. SFC values are approximations from an industry consumption chart; a specific engine may differ by ±10%, so treat the output as a close estimate, not a metered reading.

Worked examples

5 kVA home diesel set · 50% load

4 hrs/day, 30 days, Auto Diesel at the CPC default of Rs 392/L, against a 90-unit domestic bill

Real power: 5 kVA × 0.8 = 4.0 kW
Load: 4.0 kW × 50% = 2.0 kW
Fuel: 2.0 × 0.35 L/kWh = 0.70 L/hr
Cost/hr: 0.70 × Rs 392 = Rs 274.40
Cost/day: Rs 274.40 × 4 = Rs 1,097.60
Cost/month: Rs 1,097.60 × 30 = Rs 32,928.00
Per kWh: Rs 1,097.60 ÷ 8 kWh = Rs 137.20
Grid: 240 kWh on a 90-unit Domestic (D-1) bill → 330 units, Rs 1,840.00 → Rs 23,350.00
Grid per kWh: Rs 21,510.00 ÷ 240 = Rs 89.63
Generator vs grid: Rs 137.20 ÷ Rs 89.63 = 1.53×

40 kVA office diesel set · 75% load

8 hrs/day, 26 days, Auto Diesel at the CPC default of Rs 392/L, against a 1,000-unit GP-1 bill

Real power: 40 kVA × 0.8 = 32.0 kW
Load: 32.0 kW × 75% = 24.0 kW
Fuel: 24.0 × 0.28 L/kWh = 6.72 L/hr
Cost/hr: 6.72 × Rs 392 = Rs 2,634.24
Cost/day: Rs 2,634.24 × 8 = Rs 21,073.92
Cost/month: Rs 21,073.92 × 26 = Rs 547,921.92
Per kWh: Rs 21,073.92 ÷ 192 kWh = Rs 109.76
Grid: 4,992 kWh on a 1,000-unit General Purpose 1 (GP-1) bill → 5,992 units, Rs 37,600.00 → Rs 217,312.00
Grid per kWh: Rs 179,712.00 ÷ 4,992 = Rs 36.00
Generator vs grid: Rs 109.76 ÷ Rs 36.00 = 3.05×

7.5 kVA set · full load (edge case)

100% load, Auto Diesel at the CPC default of Rs 392/L

Real power: 7.5 kVA × 0.8 = 6.0 kW
Load: 6.0 kW × 100% = 6.0 kW
Fuel: 6.0 × 0.27 L/kWh = 1.62 L/hr
Cost/hr: 1.62 × Rs 392 = Rs 635.04
Per kWh: 0.27 × Rs 392 = Rs 105.84 (same as Rs 635.04 ÷ 6.0 ✓)
At full load the engine is most efficient, so Rs/kWh is at its lowest.

Frequently asked questions

Sources & references

Fuel-price defaults mirror the CPC retail figures effective October 1, 2026, read from the same table as this site's Fuel Price Today tool and last verified on 2026-10-01. Specific fuel consumption follows the industry-standard diesel-genset consumption chart (SFC ≈ 0.27–0.40 L/kWh for diesel, higher for petrol), last reviewed on 2026-07-11. The grid side is priced by this site's Electricity Bill Calculator, which follows the PUCSL tariff effective May 11, 2026 and continued by the decision of July 31, 2026, last verified on 2026-09-23. Prices are editable so you are never tied to a stale number.

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Comments & feedback

Spotted a bug or want an improvement? Tell us, our team reviews every comment, and good ideas get built. Comments are public and anonymous.

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