Miles Per Gallon Calculator

Imperial Units

UK MPG Calculator

The UK MPG Calculator works out your fuel economy using Imperial gallons, the standard for quoted MPG figures in the United Kingdom. Because a UK gallon (4.546 litres) is about 20% larger than a US gallon (3.785 litres), British MPG numbers are naturally higher than American ones for the very same vehicle — a frequent source of confusion when comparing cars across the Atlantic.

Enter the miles driven and the number of UK (Imperial) gallons used, and the tool returns your UK MPG. To make cross-border comparison easy, it also shows the US MPG equivalent, your L/100km, and km/L. UK MPG is simply miles ÷ Imperial gallons; the US figure comes from dividing by 1.20095, the ratio between the two gallon sizes.

For the metric figures, L/100km is calculated with the Imperial-specific constant 282.481 ÷ UK MPG, which builds in the larger gallon so the conversion stays accurate. This calculator is ideal if you fill up in litres but want a traditional MPG figure, if you are checking a car’s real-world economy against its advertised UK rating, or if you are comparing a UK-spec model with a US review. For everyday tracking where you record litres directly, our Miles Per Litre calculator may be quicker, and the MPG to L/100km converter handles US-gallon conversions.

How to Use

  1. Enter the miles driven since your last fill-up.
  2. Enter the number of UK Imperial gallons used.
  3. Click Calculate UK MPG (or press Enter).
  4. Read your UK MPG plus US MPG, L/100km, and km/L equivalents.

Related tools: MPG Calculator, Miles Per Litre Calculator, MPG to L/100km Converter.

Got Questions?

UK MPG Calculator FAQ

Divide the miles you drove by the number of UK (Imperial) gallons used. For example, 300 miles on 6 Imperial gallons = 50 UK MPG.

A UK Imperial gallon (4.546 litres) is larger than a US gallon (3.785 litres), so the same car covers more miles per UK gallon. To convert UK MPG to US MPG, divide by 1.20095.

Divide UK MPG by 1.20095. For example, 50 UK MPG ÷ 1.20095 ≈ 41.6 US MPG.

Use L/100km = 282.481 ÷ UK MPG. This constant already accounts for the larger Imperial gallon. So 50 UK MPG ≈ 5.65 L/100km.

The UK uses the Imperial gallon (4.54609 litres) for fuel economy figures, even though fuel is sold by the litre. That is why UK MPG figures look more favourable than US ones.