With fuel prices remaining a significant household expense, knowing how to calculate your fuel costs helps you budget effectively and make informed decisions about travel. Whether you're planning a road trip, comparing cars, or tracking your commute costs, this guide provides all the formulas and tables you need.
Unleaded Petrol
139p
Average per litre (Jan 2025)
Diesel
145p
Average per litre (Jan 2025)
How to Calculate Fuel Cost
There are two ways to calculate fuel cost depending on whether you think in MPG (miles per gallon) or L/100km (litres per 100 kilometres).
Method 1: Using MPG
Fuel Cost = (Miles ÷ MPG) × 4.546 × Price per Litre
4.546 converts gallons to litres
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Example: 150-mile journey
Car MPG: 45 mpg
Fuel price: 140p per litre (£1.40)
Calculation:
Gallons needed = 150 ÷ 45 = 3.33 gallons
Litres needed = 3.33 × 4.546 = 15.15 litres
Cost = 15.15 × £1.40 = £21.21
Method 2: Using L/100km
Fuel Cost = (Distance km ÷ 100) × L/100km × Price per Litre
Example: 200km journey
Fuel consumption: 6 L/100km
Fuel price: €1.60 per litre
Calculation:
Litres needed = (200 ÷ 100) × 6 = 12 litres
Cost = 12 × €1.60 = €19.20
Cost Per Mile Quick Reference
Use this table to quickly estimate your cost per mile based on your car's MPG:
| MPG | Cost @ 135p/L | Cost @ 140p/L | Cost @ 145p/L |
|---|---|---|---|
| 30 | 20.4p | 21.2p | 22.0p |
| 35 | 17.5p | 18.2p | 18.8p |
| 40 | 15.3p | 15.9p | 16.5p |
| 45 | 13.6p | 14.1p | 14.6p |
| 50 | 12.3p | 12.7p | 13.2p |
| 55 | 11.2p | 11.6p | 12.0p |
| 60 | 10.2p | 10.6p | 11.0p |
| 65 | 9.4p | 9.8p | 10.1p |
| 70 | 8.8p | 9.1p | 9.4p |
Common Journey Costs
Here are estimated fuel costs for popular UK journeys (assuming 45 MPG and 140p/litre):
| Journey | Distance | Fuel Cost |
|---|---|---|
| London to Birmingham | 120 miles | £16.97 |
| London to Manchester | 200 miles | £28.28 |
| London to Edinburgh | 400 miles | £56.57 |
| London to Bristol | 120 miles | £16.97 |
| Manchester to Leeds | 45 miles | £6.36 |
| Birmingham to Liverpool | 100 miles | £14.14 |
| Glasgow to Edinburgh | 47 miles | £6.65 |
| Cardiff to Bristol | 45 miles | £6.36 |
Petrol vs Diesel: Which is Cheaper?
Petrol
Price: ~139p/litre
Typical MPG: 40-50
Best for: Low mileage, short trips
Diesel
Price: ~145p/litre
Typical MPG: 50-65
Best for: High mileage, motorway driving
Break-Even Analysis
Let's compare annual fuel costs for a car doing 10,000 miles:
| Fuel Type | MPG | Price/L | Annual Cost |
|---|---|---|---|
| Petrol | 45 | 139p | £1,405 |
| Diesel | 55 | 145p | £1,199 |
| Diesel saves: | £206/year | ||
For high-mileage drivers, diesel often works out cheaper despite the higher price per litre. However, consider the purchase price difference, servicing costs, and future resale value.
Tips to Reduce Fuel Costs
- Smooth acceleration: Avoid aggressive starts and stops
- Optimal speed: 55-65mph is most fuel-efficient on motorways
- Use cruise control: Maintains steady speed on long journeys
- Engine braking: Lift off the accelerator early when approaching stops
- Avoid idling: Turn off the engine if stopped for more than a minute
Vehicle Maintenance
- Tyre pressure: Under-inflated tyres increase rolling resistance (check monthly)
- Air filter: A dirty filter reduces efficiency
- Regular servicing: Keeps the engine running optimally
- Correct oil: Use manufacturer-recommended grade
Smart Fuel Buying
- Supermarket fuel: Often 5-10p cheaper than branded forecourts
- Avoid motorway services: Premium of 15-25p per litre typical
- Price comparison apps: PetrolPrices, GasBuddy help find cheapest local fuel
- Cashback credit cards: Some offer 1-3% back on fuel purchases
- Loyalty cards: Tesco Clubcard, Nectar at Sainsbury's offer points/discounts
MPG vs L/100km Conversion
If your car shows consumption in L/100km (common for European models), here's how to convert:
MPG = 282.481 ÷ L/100km
L/100km = 282.481 ÷ MPG
| L/100km | MPG (Imperial) | Efficiency Rating |
|---|---|---|
| 4.0 | 70.6 | Excellent |
| 5.0 | 56.5 | Very Good |
| 6.0 | 47.1 | Good |
| 7.0 | 40.4 | Average |
| 8.0 | 35.3 | Below Average |
| 10.0 | 28.2 | Poor |
| 12.0 | 23.5 | Very Poor |
HMRC Mileage Rates 2025
If you use your personal car for business, you can claim these rates from HMRC:
| Vehicle Type | First 10,000 miles | Over 10,000 miles |
|---|---|---|
| Car or van | 45p per mile | 25p per mile |
| Motorcycle | 24p per mile | 24p per mile |
| Bicycle | 20p per mile | 20p per mile |
These approved mileage allowance payments (AMAP) cover fuel, wear and tear, and general running costs.
Electric vs Petrol Comparison
With electric vehicles becoming more common, here's how running costs compare:
| Factor | Petrol (45 MPG) | Electric (4 mi/kWh) |
|---|---|---|
| Cost per mile | ~14p | ~6p (home charging) |
| 100-mile journey | £14.00 | £6.00 |
| Annual cost (10k miles) | £1,400 | £600 |
| Annual savings | - | £800 |
Based on home electricity at 24p/kWh. Public rapid charging is typically 50-80p/kWh, significantly reducing the cost advantage.
Understanding UK Fuel Costs: A Deeper Look
Fuel costs represent one of the largest variable expenses for UK motorists, and understanding how they are structured can help you make smarter financial decisions. The price you pay at the pump is made up of several components: the wholesale cost of crude oil, fuel duty charged by HM Revenue & Customs, and VAT applied on top of everything including the duty itself.
As of 2025, UK fuel duty stands at 52.95 pence per litre for both petrol and diesel, though this rate has been subject to temporary reductions in recent years. On top of the base fuel price and duty, 20% VAT is added, meaning that taxes typically account for around 50-55% of the total pump price. When petrol costs 145p per litre, roughly 75p of that goes directly to the government.
The difference between petrol and diesel prices has narrowed and widened over the years. Diesel historically cost more per litre but offered better fuel economy, particularly for longer motorway journeys. However, with the shift away from diesel due to emissions concerns and clean air zones across cities like London, Birmingham, and Bristol, many drivers are reconsidering their fuel choices entirely.
Maximising Your Fuel Economy
Beyond simply finding the cheapest fuel station, there are proven techniques to reduce your overall fuel consumption. Maintaining steady speeds, keeping tyres inflated to the correct pressure (check your door sill sticker), and removing unnecessary roof boxes or heavy items from the boot can improve fuel economy by 10-15%. The RAC estimates that aggressive driving with rapid acceleration and hard braking can increase fuel consumption by up to 30% compared to smooth, anticipatory driving.
Understanding the difference between MPG (miles per gallon) and litres per 100 kilometres (l/100km) is also important. The UK traditionally uses MPG, where a higher number is better, while most European countries use l/100km, where a lower number is better. A car achieving 50 MPG uses approximately 5.65 l/100km. When comparing vehicles for purchase, always check the WLTP (Worldwide Harmonised Light Vehicle Test Procedure) figures rather than the older NEDC figures, as WLTP provides more realistic real-world fuel economy estimates.
Electric vehicles are increasingly competitive on running costs, with home charging at around 24p per kWh translating to roughly 4-6p per mile compared to 12-18p per mile for petrol cars. However, public rapid charging at 50-80p per kWh significantly reduces this advantage, making it essential to factor in your typical charging patterns when comparing costs.
Money-Saving Fuel Tips for UK Drivers
Supermarket fuel stations (Tesco, Sainsbury's, Asda, Morrisons) typically offer the cheapest prices, often 3-5p per litre less than branded stations. Using apps like PetrolPrices or Waze can help you find the cheapest fuel near your route. If you drive frequently, supermarket loyalty points on fuel purchases can add meaningful savings over a year. For a car with a 50-litre tank filled weekly, saving just 3p per litre amounts to over £78 per year.
Consider your journey planning too. Combining multiple short trips into one journey is more fuel-efficient because a warm engine operates more efficiently than a cold one. For regular commuters, car-sharing schemes can halve your fuel costs while also reducing traffic congestion and your carbon footprint.
How much does it cost to drive 100 miles in the UK?
At typical 2025 fuel prices of around 140-150p per litre and average fuel economy of 40 MPG, driving 100 miles costs approximately £16-£17 in fuel alone. More fuel-efficient cars (50+ MPG) can do it for around £13, while less efficient vehicles (25-30 MPG) may cost £22-£27. These figures don't include other running costs such as insurance, road tax, and maintenance.
Is it cheaper to fill up in the morning or evening?
There is a common myth that fuel is denser in cooler morning temperatures, giving you more energy per litre. In practice, fuel is stored underground where temperatures remain relatively constant, so the time of day makes virtually no difference. Focus instead on finding the cheapest station and driving efficiently.
What is the real-world difference between advertised and actual MPG?
Most drivers achieve 10-20% lower fuel economy than the official WLTP figures. This gap exists because real-world conditions include traffic, weather, hills, and varying driving styles that test procedures cannot fully replicate. For the most accurate personal estimate, fill your tank completely, record the mileage, and calculate your actual consumption over several fill-ups.
How does fuel duty work in the UK and how much tax is on petrol?
Is it worth switching to E10 petrol or should I use E5 super unleaded?
How can I calculate and claim business mileage for fuel costs with HMRC?
Dr. Sarah Chen, PhD
Research Scientist, Public Health
Sarah holds a PhD in Public Health from the University of Edinburgh and has published research on UK health metrics and obesity trends. She translates complex medical data into practical, accessible guidance for everyday readers.