PetrolCalculator

Fuel cost calculator

Petrol Calculator

Estimate the petrol needed for a journey and what it will cost.

Calculate your journey fuel cost

Enter your journey details, then select Calculate to see an estimated fuel cost.
Method: journey miles ÷ UK MPG × 4.54609 × price per litre. We use 4.54609 litres per UK gallon.

What your result means

Estimated cost depends on distance, UK MPG and petrol price. A longer journey, lower MPG or higher price per litre increases the cost.

Litres used and cost per mile help compare journeys or vehicles. Selecting return journey doubles distance before fuel and cost are calculated.

Example: 250-mile journey

250 miles · 45 UK MPG · 142p/litre · one way

1. Work out petrol needed

250 miles at 45 MPG gives the UK-gallon requirement, then converts it to litres.

25045×4.54609=25.26 litres\frac{250}{45}\times 4.54609 = 25.26\text{ litres}

2. Apply the petrol price

142p per litre is £1.42 per litre.

25.26×£1.42=£35.8625.26\times £1.42 = £35.86

3. Work out cost per mile

£35.86250=£0.143≈14.3p/mile\frac{£35.86}{250}=£0.143\approx 14.3\text{p/mile}

This journey needs about 25.3 litres and costs about £35.86, or 14.3p per mile.

How MPG changes the cost of the same journey

UK MPGLitresEstimated cost
3037.9 litres£53.80
4028.4 litres£40.35
5022.7 litres£32.28
6018.9 litres£26.90

What changes your journey cost?

Better fuel economy

45 → 50 MPG

£35.86 → £32.28

Saves £3.59 on this journey

Higher petrol price

142p → 150p/litre

£35.86 → £37.88

Adds £2.02 on this journey

Return journey

250 → 500 miles

£35.86 → £71.73

Approximately doubles the estimated fuel cost

How the Petrol Calculator works

Litres used=Distance in milesUK MPG×4.54609\text{Litres used}=\frac{\text{Distance in miles}}{\text{UK MPG}}\times 4.54609
Journey cost (£)=Litres used×Petrol price (p/litre)100\text{Journey cost (£)}=\text{Litres used}\times\frac{\text{Petrol price (p/litre)}}{100}
Cost per mile=Journey costJourney distance\text{Cost per mile}=\frac{\text{Journey cost}}{\text{Journey distance}}
Distance in miles=Distance in kilometres1.609344\text{Distance in miles}=\frac{\text{Distance in kilometres}}{1.609344}
Journey distance=Entered distance×2\text{Journey distance}=\text{Entered distance}\times 2

Helpful questions

Does the calculator use UK or US MPG?

This calculator uses UK / imperial MPG. A UK gallon is 4.54609 litres, while a US gallon is approximately 3.78541 litres, so UK and US MPG are not interchangeable. Use the US MPG to UK MPG Converter when you need to compare them.

How do I find my car’s real MPG?

Fill the tank, reset or record the trip mileage, then drive normally and refill. Record the miles travelled and litres added, then enter those values in the MPG Calculator. Real-world MPG can differ from manufacturer figures because everyday driving conditions vary.

Does the return journey option double the cost?

The return journey option doubles the distance you enter. With the same MPG and fuel price, the estimated litres used and cost therefore double. Actual outbound and return consumption can still differ because of real driving conditions.

Can I enter kilometres instead of miles?

Yes. Select kilometres in the calculator, and it converts the distance using 1 mile = 1.609344 km before applying the UK MPG calculation.

Why might my real fuel cost be different?

The result is an estimate based on the distance, MPG and fuel price you enter. Traffic, speed, driving style, vehicle load, tyre pressure, weather and road conditions, and climate control can all affect fuel use. Use measured real-world MPG when it is available.

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