Working out how much petrol you use is simpler than most drivers think. You need two numbers: how many miles you drive and your car's real-world fuel consumption. From those, you can calculate your weekly, monthly or annual fuel use in litres, and what it costs at current prices. Here is exactly how to do it.
The formula for working out your petrol use
The calculation has two steps. First, convert your miles into litres of fuel. Then multiply by the price per litre to get the cost.
Step 1: Miles to litres
Litres = (Miles driven / MPG) x 4.546
The 4.546 converts UK gallons to litres. MPG (miles per gallon) is your car's fuel economy figure.
Step 2: Litres to cost
Cost = Litres x price per litre / 100
Example: 7,100 miles per year, 38 MPG car, 156p per litre
(7,100 / 38) x 4.546 = 849 litres per year. 849 x 156 / 100 = £1,324 per year.
How much petrol does a typical UK driver use?
The average UK car covers around 7,100 miles per year according to the Department for Transport's National Travel Survey. Here is how much fuel that uses at different MPG figures:
| MPG | Litres per year | Litres per week | Annual cost at 156p |
|---|---|---|---|
| 50 MPG (small efficient car) | 645L | 12.4L | £1,006 |
| 40 MPG (average family car) | 807L | 15.5L | £1,259 |
| 35 MPG (typical SUV) | 921L | 17.7L | £1,437 |
| 25 MPG (large petrol / older car) | 1,290L | 24.8L | £2,012 |
How do I find out my real-world MPG?
Manufacturer MPG figures are measured under controlled laboratory conditions and are typically 10-20% better than what you achieve in real-world driving. The most accurate way to calculate your actual MPG is the brim-to-brim method:
- Fill your tank completely and note your mileage
- Drive normally until you need to refuel
- Fill up completely again and note the litres added and new mileage
- MPG = (Miles driven / Litres added) x 4.546
Alternatively, use our fuel cost calculator by registration plate. Enter your reg and it estimates your real-world MPG from your engine size and fuel type, which you can then adjust based on your driving experience.
How to reduce how much petrol you use
The most effective ways to reduce fuel consumption without modifying your car:
- Reduce motorway speed. Dropping from 70 mph to 60 mph typically improves fuel economy by 10-15%, reducing your annual fuel use significantly at higher mileages.
- Anticipate traffic. Smooth driving that avoids hard braking and sharp acceleration can improve efficiency by 10-15%.
- Check tyre pressures monthly. Under-inflated tyres increase rolling resistance and can add 1-3% to fuel consumption.
- Remove unnecessary weight. Every 50kg adds roughly 2% to fuel consumption. Empty the boot and remove roof boxes when not in use.
- Choose where you fill up. The price you pay per litre does not affect how much you use, but choosing the cheapest nearby station reduces what you spend. Use our live fuel price map to find the cheapest station near you.
Read our full guide on how to improve your MPG for 15 detailed techniques.