MPG Calculator

Work out miles per gallon, journey costs and annual fuel spend, with CO₂ and a two-car comparison. UK gallons, no sign-up.

Fills in fuel type, and annual mileage from MOT history where available. MPG is calculated from the official DVLA CO₂ figure, so real-world MPG is usually lower. Not meaningful for plug-in hybrids.

No vehicle selected. The calculators use the figures you enter below.

Summary

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Your figures

Distance (miles)

Your MPG

Fuel price (p/L)

There is no live fuel price feed. The starting price of 174.9p a litre is the UK average for unleaded petrol in the week of 5 October 2026 (diesel averaged 199.5p), from DESNZ weekly road fuel prices. Replace it with the price you paid.

Estimate

Journey cost
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Per mile
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10 miles
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Per month
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Cost comparison

Car Cost For you
Your car —
UK average (36 MPG) — —
Efficient (55 MPG) — —

Cost by distance

Insights

    Calculations use UK imperial gallons. MPG = miles ÷ gallons. 1 UK gallon = 4.54609 litres. L/100km = 282.48 ÷ MPG. Fuel cost = litres × price per litre.

    Typical economy

    Urban
    35–40 MPG
    Extra urban
    50–60 MPG
    Combined
    45–50 MPG

    MPG (miles per gallon) measures how far your car can travel on one gallon of fuel. A higher MPG means better fuel economy and lower running costs.

    In the UK, we use imperial gallons (4.54609 litres), which differs from US gallons (3.785 litres). UK MPG figures are around 20% higher than US MPG for the same vehicle.

    Official figures versus real-world MPG

    Manufacturer MPG figures are measured under test conditions, and real-world economy is often 10–20% lower. Use the Real MPG calculator to find your actual fuel economy.

    What changes MPG

    Driving style

    Aggressive acceleration and braking can reduce fuel economy by roughly 15–30% at motorway speeds and 10–40% in stop-and-go traffic. Smooth, steady driving is far more efficient.

    Tyre pressure

    Under-inflated tyres increase rolling resistance. Keeping tyres at the correct pressure can improve MPG by up to 3%.

    Vehicle weight

    Every extra 50kg reduces fuel economy by around 1–2%. Remove unnecessary items from your boot to save fuel.

    Air conditioning

    Running the AC can reduce fuel economy by 5–10%. At lower speeds, opening windows is more efficient.

    Journey type

    Motorway driving at steady speeds is typically more fuel-efficient than stop-start city driving.

    Common conversions

    European cars often display fuel consumption in L/100km (litres per 100 kilometres). Lower L/100km is better; higher MPG is better.

    MPG (UK) L/100km Efficiency
    704.0Excellent
    604.7Very good
    505.6Good
    456.3Good
    407.1Average
    358.1Average
    309.4Below average
    2511.3Poor
    2014.1Poor

    Ten habits

    1

    Drive smoothly

    Aggressive accelerating and braking can cut fuel economy by 15–30% at motorway speeds. When pulling away from lights, accelerate gently.

    2

    Read the road ahead

    Look ahead for lights, parked cars or anything that might slow you down, then ease off early instead of stopping.

    3

    Don't rev the engine

    Revving whilst stationary wastes fuel. Avoid it at lights or when parked.

    4

    Use gears sensibly

    Correct gear use can save up to 15% on fuel. Change up as soon as it is safe and practical.

    5

    Stick to the speed limit

    Driving at 80mph typically uses 15–25% more fuel than 70mph. 50mph can use up to about 25% less fuel than 70mph.

    6

    Check your tyres

    Check pressures at least every fortnight. Under-inflated tyres increase fuel use by about 3% and wear faster.

    7

    Don't idle to warm up

    Idling on cold mornings wears the engine and wastes fuel. Use de-icer and drive off once you can see clearly.

    8

    Avoid short trips

    A cold engine uses twice as much fuel as a warm one. Walk very short journeys where you can.

    9

    Use air conditioning wisely

    Use AC only when needed. At low speeds, blowers are enough. Open windows at high speed add more drag than AC.

    10

    Keep the car maintained

    Follow the service schedule. Fresh oil and clean air filters keep the engine more efficient.

    Options besides petrol and diesel

    Some need a conversion. Others are only available when you buy a new car.

    Hybrid cars

    Petrol and electric

    Hybrids combine a small petrol engine with an electric motor and battery. The Toyota Prius is the best-known example.

    The on-board computer chooses the engine, the motor, or both. A hybrid may pull away on electric power, then switch to the engine when more power is needed. They do best in stop-start city driving. On long motorway runs the advantage over a conventional petrol or diesel car is smaller.

    Electric vehicles

    100% electric

    Fully electric vehicles run on battery power with zero tailpipe emissions. The UK has a growing network of public charging points.

    Electric running costs depend on your tariff and where you charge. Home charging, especially on an off-peak tariff, is usually the cheapest option, and public rapid chargers usually cost considerably more. Range varies by model and conditions, and real-world range is usually lower than the official figure.

    Biodiesel

    Plant-based diesel

    Biodiesel is produced from plant sources such as rapeseed oil and from used cooking oil. Standard UK pump diesel already contains up to 7% biodiesel (B7). Higher blends need manufacturer approval and can affect your warranty, so check the handbook first.

    It can damage natural rubber seals and fuel lines on older vehicles, so check compatibility first. Depending on the feedstock, biodiesel can have lower lifecycle emissions than fossil diesel.

    LPG (Autogas)

    Liquefied petroleum gas

    LPG is a mixture of propane and butane. It is sold at a limited number of refuelling sites in the UK, so check the stations on your usual routes before converting.

    Many petrol cars can be converted, but conversion costs vary by vehicle and installer, so get quotes. LPG is usually cheaper per litre than petrol, but you use more litres per mile, so compare the saving at current prices. High-mileage drivers are the most likely to recoup the conversion cost, and LPG can produce lower tailpipe CO₂ than petrol.

    Can I find my car's MPG by registration number?
    Yes, for petrol and diesel cars. The tool takes the vehicle's official DVLA CO₂ figure (g/km), converts it to fuel use with a standard factor for petrol or diesel, and gives a calculated MPG. This is an official-style figure rather than a real-world one, so your actual MPG is usually lower, and it is not meaningful for plug-in hybrids. Annual mileage is estimated from MOT history where available. The results fill in the calculators above.
    How do I calculate MPG?
    Divide miles driven by gallons used. For UK imperial gallons: MPG = miles driven ÷ gallons used. If you know litres, divide by 4.54609 first. Or enter distance, fuel spend and price per litre in the calculator.
    How do I compare MPG between two cars?
    Use Compare Cars to enter each vehicle's MPG, your annual mileage and the fuel price. It shows the fuel cost for each car and how much you could save by choosing the more efficient one.
    What is a real MPG calculator?
    It works out on-the-road fuel economy from fuel bought and miles driven, not manufacturer WLTP figures. Real-world MPG is often 10–20% lower than official figures. The Real MPG tab uses your fuel receipts.
    How do I calculate miles per gallon in the UK?
    UK gallons are imperial (4.54609 litres), not US gallons (3.785 litres). Fill the tank, note the mileage, refuel, then divide miles by litres and multiply by 4.54609. Or enter spend, price per litre and distance in the calculator.
    How do I convert MPG to L/100km?
    Divide 282.48 by the MPG figure. For example, 40 MPG = 282.48 ÷ 40 = 7.06 L/100km. To convert L/100km to UK MPG, divide 282.48 by the L/100km figure. The Convert tab does this instantly.
    How much does it cost to drive 100 miles?
    As an example, at 175p per litre and 38 MPG, 100 miles costs about £21. A 60 MPG car is around £13.30; a 30 MPG car around £26.50. Fuel prices vary by station and over time, and this tool has no live price feed, so use the price you paid. Journey Cost gives exact figures.
    Does driving slower save fuel?
    Yes. Driving at 70mph can use up to 25–30% more fuel than 50mph, and 80mph typically uses 15–25% more than 70mph. The RAC puts the most efficient speed for most cars at around 45–50mph in the highest practical gear. Smooth acceleration still saves more than speed alone.
    Does air conditioning affect fuel consumption?
    Yes. The US Department of Energy reports a 5–25% drop depending on conditions. Below about 40mph, opening windows is usually more efficient. Above around 60mph, window drag typically uses more fuel than the AC.
    How much fuel does idling use?
    A typical car uses 0.5–1 litre per hour when idling, or roughly 1–2p per minute. Argonne National Laboratory found that 10 seconds of idling can use more fuel than restarting. Many modern cars use stop-start for this reason.
    Is diesel more fuel efficient than petrol?
    Diesels typically return around 20–30% better MPG than equivalent petrol cars on paper, with a smaller gap in town driving. Diesel costs more per litre and diesel cars cost more to buy, so diesel suits high-mileage drivers best, especially on motorways.

    Check your vehicle's full details

    Get official MPG figures, emissions data, tax band and more with a free vehicle check. You can also check ULEZ status.

    Check a vehicle