Miles Per Gallon Calculator

Petrol Vehicles

Petrol MPG Calculator

The miles per gallon calculator petrol tool works out the real-world fuel economy of your petrol car from the miles you've driven and the fuel you've used. Manufacturer figures come from lab tests; this calculator shows what your car actually achieves on your roads and with your driving style.

Enter your miles and petrol used in US gallons, UK gallons, or litres. The result is labelled US MPG or UK MPG to match your unit, and the calculator also doubles as a miles per litre calculator petrol, returning miles per litre and L/100km so UK drivers buying fuel in litres can read economy in any form.

Petrol emits about 2.31 kg of CO₂ per litre burned — less than diesel's 2.68 kg — and the calculator estimates CO₂ per tank so you can weigh efficiency against emissions. Add a price per unit to get cost per mile. For the most reliable reading, use the brim-to-brim method over a full tank rather than a single short trip.

How to Use

  1. Enter the miles driven.
  2. Choose your fuel unit: US gallons, UK gallons, or litres.
  3. Enter the petrol used.
  4. Optionally add the petrol price per unit.
  5. Click Calculate Petrol MPG (or press Enter).

Related tools: MPG Calculator, Diesel MPG Calculator, MPG Calculator UK, Miles Per Litre Calculator.

Got Questions?

Petrol MPG Calculator FAQ

Fill up completely, drive until you need fuel again, fill up completely a second time. Divide the miles driven between fill-ups by the gallons used on the second fill. That’s your MPG.

In UK figures, 40–50 MPG is good for a petrol car. 50+ is excellent. City driving will always be lower than motorway. Most modern petrol cars achieve 35–50 UK MPG (29–42 US MPG).

Manufacturer MPG figures come from lab tests. Real-world driving — cold starts, air conditioning, traffic, speed variation, and tyre pressure — reduces economy by 10–25%.

Petrol releases approximately 2.31 kg of CO₂ per litre burned. A car averaging 40 UK MPG (7.05 L/100km) emits roughly 163g CO₂/km.

Yes. Higher-octane fuel (e.g. 97–99 RON premium petrol) can improve MPG slightly in engines tuned for it, typically 2–4%. Regular 95 RON is sufficient for most cars.