MotorBabuCNG vs petrol cost calculator
Is a CNG car worth it for how much you drive? Compare the fuel cost per km, your monthly saving, and how soon the extra price of the CNG version pays for itself.
How the calculation works
- Cost per km = fuel price ÷ mileage, for petrol (₹/L ÷ km/l) and CNG (₹/kg ÷ km/kg).
- Monthly saving = (petrol cost per km − CNG cost per km) × km a month.
- Payback = extra cost of the CNG version ÷ monthly saving.
Use your own real mileage, not the brochure figure — the mileage calculator works it out from a full-tank fill. Fuel prices differ a lot between cities, so enter today's prices where you fill up.
Beyond fuel: what else to weigh
- Maintenance: CNG engines are harder on spark plugs and oil — for example, Maruti replaces CNG spark plugs every 50,000 km against 1,00,000 km on petrol — and the CNG kit needs periodic servicing.
- Cylinder hydro-test: the CNG cylinder must be re-tested at fixed intervals; the next test date is on the cylinder's plate.
- Boot space: the cylinder usually takes up much of the boot.
- Refuelling: CNG stations are fewer, and queues can be long in some cities.
Keep your CNG car's schedule on track
MotorBabu has a CNG schedule built in — oil changes, CNG kit service and the cylinder hydro-test — and logs your fuel fills to show your real cost per km. Free, no ads.
Questions people ask
How do I compare CNG and petrol running costs?
Work out the cost per km of each: fuel price ÷ mileage. Petrol at ₹105 a litre and 18 km/l is ₹5.83 a km; CNG at ₹90 a kg and 26 km/kg is ₹3.46 a km. Multiply the difference by how far you drive.
Why is CNG mileage in km/kg?
CNG is sold by weight, so mileage is measured in kilometres per kilogram. Compare costs per km, not the mileage figures themselves.
How long does a CNG car take to pay back its extra price?
Divide the extra cost (the CNG variant's higher price, or the kit cost) by your monthly saving. The more you drive, the sooner it pays back — the calculator works it out.
Does a CNG car cost more to maintain?
A little. CNG engines run hotter: Maruti's manuals, for example, replace spark plugs every 50,000 km on CNG versus 1,00,000 km on petrol, and the CNG kit needs periodic servicing. The cylinder also needs a hydro-test at fixed intervals — the due date is on the cylinder's test plate. MotorBabu's CNG schedule covers these.
Can I fit a CNG kit to my petrol car?
Only an approved kit, fitted by an authorised dealer, and the conversion must be endorsed on your RC at the RTO. Tell your insurer too, or a claim can be refused.
Does a CNG car still use petrol?
Most CNG cars are bi-fuel: they can start or run on petrol and switch to CNG. The calculator assumes you drive on CNG almost all the time.