If you want to quickly estimate how much your car costs to fuel in the UK, this mpg cost calculator does the hard work for you. Enter your annual miles, your car's mpg, and the current fuel price in pence per litre. You will instantly see your cost per mile, monthly fuel budget, annual spend, and optional trip cost.
How to use this UK mpg calculator
- Annual mileage: Total miles you drive each year.
- MPG UK: Your vehicle efficiency in imperial miles per gallon.
- Fuel price: Pump price in pence per litre (e.g., 149.9).
- Trip distance: Optional one-off trip estimate.
Press Calculate running cost and the calculator returns practical numbers you can use for budgeting, commuting decisions, and comparing vehicles.
Formula used by the calculator
The calculator uses standard UK conversion values:
- 1 imperial gallon = 4.54609 litres
- Litres used per mile = 4.54609 ÷ MPG (UK)
- Cost per mile = litres per mile × (fuel price in pounds per litre)
- Annual fuel cost = cost per mile × annual miles
Worked example
Suppose you drive 10,000 miles/year, your car averages 45 mpg (UK), and fuel is 145p/litre:
- Litres per mile ≈ 4.54609 / 45 = 0.1010 L
- Cost per mile ≈ 0.1010 × £1.45 = £0.146
- Annual fuel cost ≈ £0.146 × 10,000 = £1,464
That gives a fast benchmark for whether a more efficient car could save you money over time.
UK mpg vs US mpg: why it matters
A common mistake is entering US mpg figures into a UK calculator. UK mpg (imperial) and US mpg are not the same because the gallon size is different. Imperial gallons are larger, so UK mpg numbers are always higher than equivalent US mpg values.
| Measure | Value |
|---|---|
| 1 UK gallon | 4.54609 litres |
| 1 US gallon | 3.78541 litres |
| Convert UK mpg to US mpg | Multiply by 0.8327 |
What impacts your real-world fuel cost?
Official mpg is useful, but your actual fuel spend can vary significantly:
- Driving style: Harsh acceleration and high motorway speeds increase consumption.
- Traffic conditions: Stop-start urban driving lowers mpg.
- Tyre pressure: Underinflated tyres increase rolling resistance.
- Vehicle load: More weight means more fuel burned.
- Weather: Cold weather and short trips reduce efficiency.
- Fuel prices: UK pump prices can change weekly.
Quick ways to lower fuel spend
- Drive smoothly and anticipate braking.
- Keep tyres correctly inflated.
- Remove unnecessary weight from the boot.
- Plan journeys to avoid heavy traffic where possible.
- Compare fuel prices locally before filling up.
- Service your vehicle regularly (air filter, spark plugs, oil).
Frequently asked questions
Is this calculator for petrol and diesel?
Yes. The core fuel cost math works for both. The fuel type selector is used for a rough annual CO₂ estimate.
Can I use it for vans and company cars?
Absolutely. As long as you know your mpg and annual mileage, the calculator will provide a good budget estimate.
Does this include insurance, tax, and maintenance?
No. This tool calculates fuel cost only. For true running cost, also include insurance, VED, servicing, tyres, finance, and depreciation.
How accurate is it?
It is a solid estimate based on your input values. If your real mpg varies with driving conditions, your real spend will vary too.
Final thoughts
A simple mpg cost calculator UK can be surprisingly powerful. It helps you make practical decisions: whether to switch cars, reduce commute costs, or set a realistic monthly driving budget. Use it regularly with up-to-date fuel prices and you'll have a clearer picture of what every mile really costs.