MPG Calculator UK

Work out your true miles per gallon and cost per mile. Enter the miles driven since your last fill-up, the litres dispensed and the price per litre, and the calculator gives you your real-world MPG and what each mile actually costs.

MPG Calculator

How to calculate miles per gallon

The formula for MPG is simple: divide the miles you drove by the gallons of fuel you used. Since UK pumps dispense in litres, you first convert litres to gallons by dividing by 4.54609 (the imperial gallon).

MPG = miles driven ÷ (litres used ÷ 4.54609)

For example, if you drove 350 miles on 40 litres: 40 ÷ 4.54609 = 8.80 gallons, then 350 ÷ 8.80 = 39.8 MPG.

The most accurate way to measure is the brim-to-brim method: fill your tank completely, zero the trip meter, drive normally, then fill up again. The litres shown on the pump and the miles on your trip meter give you exact figures with no guesswork.

What is a good MPG?

Vehicle typePoorAverageGoodExcellent
Small petrol (e.g. Fiesta, Corsa)< 3535–4545–5555+
Medium petrol (e.g. Golf, Focus)< 3030–4040–5050+
Large petrol / SUV< 2525–3535–4040+
Diesel (any size)< 4040–5050–6060+
Hybrid< 4545–5555–7070+

These are real-world figures, not manufacturer claims. If your MPG is consistently below the "poor" range, it could indicate a maintenance issue such as underinflated tyres, a dirty air filter, or a fault with the engine management system.

Tips to improve your fuel economy

  • Tyre pressure — check monthly. Underinflation by just 10 psi can cost 2–3 MPG.
  • Smooth driving — accelerate gently, anticipate braking and shift up early. Aggressive driving can reduce MPG by 15–30%.
  • Speed — 60 mph vs 70 mph can improve fuel economy by 10–15%. Motorway cruising at high speed is the biggest single fuel drain.
  • Remove drag — roof racks and boxes when not in use. A roof box at 70 mph can add 15% to fuel consumption.
  • Reduce weight — clear out unnecessary items from the boot. Every 50 kg costs roughly 1–2% in fuel economy.
  • Engine maintenance — regular servicing, clean air filters and fresh oil all help the engine run efficiently.

Converting between MPG and litres per 100 km

Many European cars and hire vehicles quote fuel consumption in litres per 100 km (L/100 km). To convert to UK imperial MPG:

MPG = 282.48 ÷ L/100 km

For example, 6 L/100 km = 282.48 ÷ 6 = 47.1 MPG. Note: this gives imperial MPG (UK gallons). US MPG uses a smaller gallon, so the same car would show a lower MPG number in the US.

Related calculators

Frequently Asked Questions

MPG stands for Miles Per Gallon — a measure of how far your car travels on one gallon of fuel. The higher the MPG, the more fuel-efficient your car.

Divide the miles driven by the gallons used. Since UK pumps sell litres, the formula is: MPG = miles ÷ (litres ÷ 4.54609). The easiest method: fill up completely, zero your trip meter, drive normally, then fill up again. Enter the miles and litres into the calculator above for an instant result.

No. Official WLTP figures are measured under laboratory conditions and are typically 15–25% higher than real-world driving. Older NEDC figures can be 30% or more too high. Always calculate your own MPG for an accurate picture of what your car actually achieves.

For a petrol car, 40 MPG or above is considered good; over 50 MPG is excellent. Diesel cars typically achieve higher MPG figures — 50+ is common, with efficient models exceeding 60 MPG. Hybrids routinely see 55–70 MPG in mixed driving.

Divide 282.48 by the L/100 km figure. For example, 5 L/100 km = 282.48 ÷ 5 = 56.5 MPG (imperial). This is the UK gallon — the US gallon is smaller, so US MPG numbers are always lower for the same car.

Official tests use ideal conditions — warm engine, no wind, flat road, moderate speed. Real driving includes cold starts, hills, traffic, air conditioning and higher motorway speeds. Short journeys are the biggest factor: a cold engine uses significantly more fuel for the first few miles.

Keep tyres at the correct pressure (underinflation alone costs 2–3 MPG). Accelerate gently, shift up early, anticipate braking, remove roof racks when not in use and avoid idling. Keeping your speed at 60 mph instead of 70 mph can improve fuel economy by 10–15%.