Kalkulo

Fuel consumption calculator

Work out your real-world MPG (imperial gallon) or L/100km from miles driven and fuel used, plus the cost of a trip at the current pump price.

Result
39.8 MPG
Trip cost : £59.20

About this tool

Why use this tool

Fuel costs represent a major recurring expense for British motorists. The AA estimates the average UK household spends around £1,900 per year on petrol or diesel. With unleaded around 145p/litre and diesel around 152p/litre in 2026 (down from 2022 peaks but well above pre-2020 levels), understanding your real MPG (imperial) or L/100km lets you budget journeys, compare cars before buying and track eco-driving progress.

How it works

MPG (imperial) = Miles driven / Imperial gallons used (1 imperial gallon = 4.546 litres, ~20% larger than the US gallon). L/100 km = (Litres × 100) / Kilometres. Since September 2018, the WLTP (Worldwide Harmonised Light Vehicles Test Procedure) replaced the older NEDC cycle for European homologation, providing more realistic figures. Real-world consumption is typically 10-20% higher than WLTP, per What Car? True MPG testing.

Real example

A 400-mile round-trip from London to the Lake District in a diesel saloon rated 55 mpg (imperial) uses about 7.3 gallons = 33.1 litres at 152p = £50.30. The same trip in a large petrol SUV rated 32 mpg uses 12.5 gallons = 56.8 litres at 145p = £82.36. Over a year of similar getaways (10 round-trips), the SUV costs £320 more. A plug-in hybrid at 3.5 L/100 km would cost around £25 in fuel plus a home charge.

Practical tips

To improve MPG: keep tyres inflated to the doorpost spec (RAC estimates under-inflation cuts economy by up to 3%), drive at 60-65 mph on motorways instead of 75+ (the Department for Transport estimates 25% fuel saving at 60 mph vs. 80 mph), remove roof boxes and roof bars when not in use, use engine-braking rather than the footbrake in traffic, and combine short trips. The Plug-in Car Grant ended in 2022, but electric vehicles remain zero-rated for VED for 2026 (subject to change from April 2025 under the current government schedule).

Disclaimer

UK fuel prices vary daily depending on Brent crude, fuel duty (57.95p/litre plus 20% VAT in 2026, subject to Autumn Budget review) and forecourt margins. Check current pump prices via the RAC Fuel Watch or PetrolPrices.com. Manufacturer MPG figures follow WLTP homologation; actual mileage varies with driving style, load, weather and journey type. This tool is not affiliated with HMRC, DVLA, DVSA or the RAC Foundation.

Frequently asked questions

Why is the imperial MPG figure higher than a US MPG figure for the same car?⌄
An imperial gallon (4.546 litres) holds about 20% more fuel than a US gallon (3.785 litres), so the same real-world fuel efficiency produces a bigger 'miles per gallon' number when measured in imperial gallons. A car quoted at 47 mpg in the UK and 39 mpg in a US road test can be burning fuel at exactly the same rate.
What changed when WLTP replaced the old NEDC test?⌄
The Worldwide Harmonised Light Vehicles Test Procedure (WLTP) replaced the New European Driving Cycle (NEDC) for UK and EU type approval from September 2018, using more realistic speeds, accelerations and test conditions. NEDC figures were widely criticised for overstating real-world economy, so WLTP numbers, while still optimistic, sit closer to what drivers actually see.
How much worse is real-world MPG than the WLTP figure?⌄
Independent testing such as What Car?'s True MPG programme typically finds real-world consumption running 10-20% higher than the official WLTP figure, with the gap widest for smaller turbocharged petrol engines driven hard. Motorway cruising at a steady speed tends to come closest to the homologated number.
Does removing a roof box or roof bars actually save fuel?⌄
Yes — a roof box adds significant aerodynamic drag, and the RAC and other UK motoring bodies estimate it can cut motorway fuel economy noticeably, more than most drivers expect for a single accessory. Removing it when not in use, along with unused roof bars, is one of the simplest ways to improve motorway MPG.
How do I convert between MPG and litres per 100km when comparing cars?⌄
For an imperial MPG figure, divide 282.5 by the L/100km figure to get MPG, or divide 282.5 by the MPG to get L/100km — the two units are inversely related. This calculator converts automatically between them, which is useful when comparing a UK-spec car's MPG rating against a continental European listing quoted in L/100km.

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