Fuel Saving & Economy
MPG
How to work out miles per gallon
CheckFuelPrices Editorial
Expert Written • 4 industry sources
To work out your miles per gallon (MPG), brim your tank, drive a measured distance, brim it again, then divide the miles driven by the litres you added and multiply by 4.546. This gives you your real-world MPG, which is often lower than the official manufacturer figure.
The Step-by-Step MPG Calculation
Step 1 – Fill up completely:
Brim your tank to the very top and reset your trip odometer to zero. This is your starting point.
Step 2 – Drive normally:
Drive as you usually would for at least 100 miles to get a representative result. The larger the sample distance, the more accurate your MPG figure.
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Step 3 – Fill up again and note the litres:
Brim the tank again and record exactly how many litres you put in. Also note the miles on your trip odometer.
Step 4 – Apply the formula:
Divide the miles driven by the litres used, then multiply by 4.546 (one UK gallon). For example: 300 miles ÷ 40 litres × 4.546 = 34.1 MPG.
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Why Your Real MPG Differs from Official Figures
Official figures are lab-tested:
Manufacturers test fuel consumption under controlled laboratory conditions using the WLTP cycle, which does not fully reflect real-world driving in traffic, cold weather, or with a full load.
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Real-world MPG is typically lower:
Most drivers achieve 10–20% fewer MPG than the official figure. Short trips, motorway driving at high speed, and air conditioning use all reduce economy.
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Check your car's official figure:
GOV.UK publishes official fuel consumption data for every model sold in the UK, which is useful as a benchmark to compare against your calculated figure.
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How to Improve Your MPG
Smooth acceleration and braking:
Anticipating the road ahead and avoiding harsh acceleration or heavy braking is the single biggest factor in improving real-world fuel economy.
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Keep tyres properly inflated:
Under-inflated tyres increase rolling resistance, which burns more fuel. Check tyre pressure monthly against your vehicle's recommended PSI.
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Remove unnecessary weight:
Every extra 50 kg in your car increases fuel consumption by around 2%. Remove roof racks and heavy items from the boot when not needed.
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Cut Your Fuel Costs Once You Know Your MPG
A lower MPG means higher fuel spend:
Once you know your real MPG, even a 1–2p per litre saving at the pump makes a measurable difference over a full year of driving.
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Find the cheapest station near you:
CheckFuelPrices shows live petrol and diesel prices at 4,000+ UK stations, updated every 30 minutes using CMA government open data, so you can fill up for less every time.
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Sources
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