Petrol vs Diesel Calculator

About this calculator

A diesel usually costs more to buy, goes further on a litre, and pays the difference back over distance — if you drive far enough. How far is the whole question, and it depends on four numbers that differ by vehicle, by state and by month.

This page takes all four from you. It has no table of mileages and no idea what fuel costs where you live, which is deliberate: both change often enough that a stored figure would be wrong more often than right.

How to use this calculator

1. Enter how far you drive in a year. This is the number that decides the answer.
2. Enter the mileage each version returns. Use owner figures rather than brochure ones where you can get them, and make sure both are measured the same way.
3. Enter both pump prices from a station near you.
4. Enter how much more the diesel costs on the road, if it costs more.

The formula

Cost per km   = Price per litre / Mileage        (for each fuel)
Yearly cost   = Cost per km x Distance
Difference    = the larger yearly cost - the smaller
Break-even km = Extra up-front cost / (difference in cost per km)

Running cost is compared per kilometre rather than per litre, because the two fuels are not priced or consumed at the same rate and the per-litre price on its own tells you nothing.

Worked example

15,000 km a year; petrol 15 km/L at ₹105, diesel 20 km/L at ₹92; diesel ₹1,50,000 dearer:

Petrol = 105 / 15 = 7.00 per km -> 1,05,000 a year
Diesel =  92 / 20 = 4.60 per km ->   69,000 a year
Saving = 36,000 a year
Break-even = 1,50,000 / 2.40 = 62,500 km

That is a little over four years at this distance — and the answer changes completely if you drive 5,000 km a year instead.

Notes and limits

• This compares fuel only. Diesel servicing is often dearer, diesel particulate filters need regular highway running to stay healthy, and resale values differ. None of that is here.
• Several Indian cities restrict older diesel vehicles. A break-even ten years out is not really a break-even if the vehicle cannot be used for all ten.
• Short urban trips suit diesels badly. If most of your driving is a few kilometres at a time, the mileage advantage will be smaller than the brochure gap suggests.
• The gap between petrol and diesel pump prices has narrowed considerably in India over the past decade and is not a constant. Use today's prices and re-run it when they move.

What this calculation assumes

• Fuel only. Servicing, insurance, resale and any usage restrictions are not compared.
• Both mileages and both prices are figures you entered; nothing is assumed about either fuel.
• Prices and mileages are taken as constant over the period.