With E20 petrol now the only petrol sold in India (since April 2026) and its 2-5% mileage penalty on top of already-higher petrol prices, many drivers are comparing running costs against CNG and diesel. This calculator lets you plug in your own fuel prices, mileage, and monthly distance to see exactly which fuel is cheapest for you — not just the national average.
E20 Petrol vs CNG vs Diesel Running Cost Calculator
E20 Petrol
Diesel
CNG
How the Running Cost Comparison Works
Step 1: Cost Per KM for Each Fuel
Cost per KM = Fuel Price / Mileage E20 Petrol: Rs.103 / 15 km/L = Rs.6.87/km Diesel: Rs.94 / 20 km/L = Rs.4.70/km CNG: Rs.85 / 22 km/kg = Rs.3.86/km
Step 2: Monthly Cost
Monthly Cost = Cost per KM x Monthly Distance At 1,500 km/month: Petrol Rs.10,305 | Diesel Rs.7,050 | CNG Rs.5,790
National Average Reference Table (July 2026)
| Fuel | Typical Price | Typical Mileage | Approx Cost/KM |
|---|---|---|---|
| E20 Petrol | Rs.102–116/L | 13–18 km/L | Rs.6–8/km |
| Diesel | Rs.89–102/L | 18–24 km/L | Rs.4–5.5/km |
| CNG | Rs.83–109/kg | 18–25 km/kg | Rs.3.3–5/km |
Prices vary significantly by city (e.g. CNG ranges from ~Rs.83/kg in Delhi to ~Rs.109/kg in Hyderabad) — always use your local price in the calculator above rather than the national average.
Frequently Asked Questions
Is CNG really cheaper than E20 petrol?
Yes, in most Indian cities CNG costs roughly 50-60% less per km than petrol, even accounting for CNG’s slightly lower per-kg mileage compared to petrol’s per-litre mileage. This gap has widened slightly since E20 reduced petrol mileage further.
Is diesel or CNG cheaper to run?
CNG is usually 15-20% cheaper per km than diesel, since CNG’s price per unit is lower even though diesel vehicles often get slightly better mileage per unit of fuel.
Does E20’s mileage drop make petrol cars more expensive to switch away from?
Yes — since E20 typically cuts petrol mileage by 2-5% (more for older vehicles) without lowering the pump price, the cost-per-km gap between petrol and CNG/diesel has widened compared to the pre-E20 era. Use our E20 Mileage & Cost Calculator to see your exact mileage drop first, then plug that into this comparison.
Should I convert my petrol car to CNG?
If you drive high monthly distances, CNG conversion can pay for itself through fuel savings within 1-2 years for many vehicles — run your own numbers in the calculator above using your actual monthly km to estimate the savings before deciding.
Sources
- V3Cars — CNG Prices in India by City
- IOAGPL — CNG vs Petrol vs Diesel: Cost, Mileage & Emissions Comparison
- THINK Gas — How CNG Saves You Money: Cost Analysis
Conclusion
CNG is generally the cheapest fuel to run per km in India, followed by diesel, with E20 petrol now the most expensive due to its mileage penalty on top of already-higher prices. Your exact numbers depend on local fuel prices and your vehicle’s real mileage — use the calculator above with your own figures, and check our E20 Mileage Calculator and E20 Compatibility Checker for the full picture. Also see our E20 vs Premium Petrol (XP95/XP100) Cost Calculator. Also see our E20 Fuel Additive & Octane Booster ROI Calculator.