What is MPG?
MPG is a quick way to compare how far a petrol or diesel car can travel on a set amount of fuel. It matters because a small MPG difference can change the real cost of every journey.
MPG stands for miles per gallon. It shows how many miles a vehicle can travel using one UK gallon of fuel.
The higher the MPG, the less fuel the car normally uses for each mile. That is why MPG is one of the simplest ways to compare petrol and diesel running costs before you calculate the actual pounds-and-pence journey cost.
Why MPG matters
MPG turns fuel use into something easy to compare. A car that returns 50 MPG should usually cost less to fuel than a similar car returning 35 MPG, assuming both use the same fuel price and cover the same distance.
It is also the bridge between technical vehicle efficiency and real-world costs. Once you know a car’s MPG, you can estimate litres used, journey cost, annual fuel spend and pence per mile.
Turn MPG into a journey cost
Use the fuel cost calculator to estimate litres used, total trip cost and cost per mile.
How MPG is calculated
MPG is calculated by dividing the number of miles driven by the number of UK gallons of fuel used.
MPG = miles driven ÷ UK gallons usedBecause UK fuel is usually bought in litres, you often need one extra step. One UK gallon is 4.54609 litres, so litres must be converted into UK gallons before calculating MPG.
UK gallons used = litres used ÷ 4.54609
MPG = miles driven ÷ UK gallons usedWorked example
Suppose you drive 300 miles and use 35 litres of fuel.
35 litres ÷ 4.54609 = 7.70 UK gallons
300 miles ÷ 7.70 = 38.95 MPGThe MPG calculator does this conversion automatically, so you can enter either litres or UK gallons.
MPG is not the same as cost per mile
MPG tells you fuel efficiency. Cost per mile tells you how much each mile costs in money. A high-MPG car can still cost more to run if the fuel price is high, the car is driven hard, or most journeys are short stop-start trips.
| Metric | What it tells you | Best calculator |
|---|---|---|
| MPG | How far a car travels on one UK gallon of fuel. | MPG calculator |
| Fuel cost | The estimated petrol or diesel cost for a journey. | Fuel cost calculator |
| Commute cost | The weekly, monthly and annual cost of driving to work. | Commute cost calculator |
| EV cost per mile | The electricity cost of driving an electric car. | EV charging cost calculator |
Typical MPG ranges
Real-world MPG varies by vehicle, engine, tyres, weather, route and driving style. Manufacturer figures can be useful for comparison, but your actual MPG may be lower or higher.
| Vehicle / use case | Broad MPG range | What to watch |
|---|---|---|
| Small petrol car | 40–60 MPG | Short urban trips can reduce efficiency. |
| Diesel motorway car | 45–70 MPG | Best on longer steady-speed journeys. |
| SUV or larger petrol car | 25–45 MPG | Weight and aerodynamics can increase fuel use. |
| Hybrid | 40–70+ MPG | Results depend heavily on journey type and battery use. |
Common MPG mistakes
- Using US gallons: UK MPG and US MPG are not the same because the gallon size is different.
- Trusting one trip too much: one journey can be distorted by traffic, weather, hills or heavy loads.
- Ignoring fuel price: MPG does not include petrol or diesel price, so it does not show total cost on its own.
- Comparing EVs with MPG: electric cars are usually compared using miles per kWh, not MPG.
MPG FAQs
Is higher MPG better?
Usually, yes. Higher MPG normally means the car travels further on the same amount of fuel, which can reduce fuel cost per mile.
Is MPG based on litres or gallons?
MPG is based on gallons, but UK fuel is sold in litres. That is why a litres-to-UK-gallons conversion is needed when calculating MPG from fuel receipts.
Why is my real MPG lower than advertised?
Advertised figures are measured under standardised test conditions. Real driving can include colder weather, traffic, short journeys, roof boxes, heavy loads and faster acceleration.
Can electric cars have MPG?
Electric cars are usually compared using miles per kWh or cost per mile. Some plug-in hybrids may show MPG, but the result can be misleading if electric-only miles are included.