Guides / Fuel and EV costs (UK)
UK fuel economy and running costs explained
Last updated July 2026. For education only; not financial advice.
Why UK fuel figures confuse people
British drivers still talk in miles per gallon, but fuel is sold by the litre and official economy tests use metric units internally. Worse, the UK imperial gallon (about 4.55 litres) is larger than the US gallon, so an identical car shows higher MPG in Britain than in America. When you compare brochure figures, check whether they are WLTP combined cycle numbers and remember that real-world driving is usually worse than the lab — often 10–20% for petrol and diesel, sometimes more in cold weather or stop-start traffic.
Petrol and diesel: the inputs that matter
To estimate trip cost you need three things: distance, your actual or expected fuel economy in UK imperial MPG, and the price per litre at the pump you use. Our fuel and EV cost calculator handles the unit conversions. Diesel often achieves higher MPG on motorways but may cost more per litre and can face higher urban charges in some cities. Fuel duty and VAT are set nationally, but forecourt prices vary by location and brand.
Electric cars: miles per kWh
EV efficiency is commonly expressed as miles per kilowatt-hour (mi/kWh). A car achieving 4 mi/kWh on a 60 kWh usable battery might travel roughly 240 miles in ideal conditions — but heating, motorway speed, roof boxes, and battery age all reduce range. Charging cost depends on where you plug in: home off-peak tariffs are often far cheaper per mile than rapid public chargers. Include standing charges on your electricity bill if you want a household view, not just the marginal cost of one journey.
Comparing petrol and electric fairly
Running cost is only part of total cost of ownership. Purchase price, finance, insurance, tax bands, maintenance, tyres, depreciation, and charging equipment all matter. A lower pence-per-mile figure does not automatically mean a cheaper car over five years. Run separate scenarios with realistic MPG and mi/kWh for your routes — commute vs long holiday drives — rather than a single brochure number.
Tips for improving real-world economy
Tyre pressure, roof racks, aggressive acceleration, and unused weight in the boot all hurt efficiency. For EVs, pre-conditioning while plugged in and using eco modes on familiar routes can help. None of this replaces safety or reasonable journey times; the goal is informed expectations, not hypermiling extremes.
Related tools and terms
Estimate a specific journey with the fuel cost tool. Convert between metric and imperial units with the unit converter. See glossary entries for MPG (UK imperial) and miles per kWh.