Petrol and CNG ownership costs depend on more than the price displayed at a filling station. Annual distance, local fuel availability, vehicle efficiency, conversion quality, maintenance and usable luggage space all influence which option is more practical for a particular driver.
This guide explains product and selection principles. It does not confirm compatibility, replace model-specific documents or provide a repair procedure.
CNG vs petrol mileage: compare cost per kilometre, not unlike units
Petrol mileage is measured in km/l and CNG mileage, or CNG car average, is measured in km/kg, so the headline numbers are not directly comparable. Measure each fuel on broadly comparable routes and use current local prices to calculate cost per kilometre. Treat manufacturer figures as labelled exact-variant claims and real-world measurements as vehicle- and condition-specific.
Compare CNG vs petrol running cost per km
For standard petrol-injection applications using Conventional or Sequential CNG, MIJO's general thumb rule estimates CNG mileage in km/kg at approximately 1.5 times actual petrol mileage in km/l. Use measured mileage where available. CNG running cost per km = current local CNG price per kg ÷ measured CNG mileage in km/kg. Petrol running cost per km = current local petrol price per litre ÷ measured petrol mileage in km/l. Compare both using the same city, price date and broadly comparable routes, then add conversion, inspection, service and other ownership costs relevant to the vehicle. Keep all inputs editable; neither fuel is guaranteed to be cheaper for every owner. This standard thumb rule cannot be applied to Direct Injection (DI) engines. Select Direct Injection in the vehicle-specific savings calculator to estimate savings for your vehicle.
Allow for the whole ownership picture
A CNG vehicle may add costs for conversion, inspections and gas-system servicing, while petrol-only operation avoids that additional hardware. CNG availability, refill queues, cylinder space and the proportion of driving actually completed on gas can materially change the outcome.
Maintenance depends on the vehicle and system
Both options require routine engine care. A converted car also needs attention to filters, hoses, valves, calibration and cylinder-related checks, and poor installation can create avoidable faults; compare written service requirements rather than assuming either fuel always costs less to maintain.