How do I calculate fuel cost for a trip?

Divide the trip distance by your MPG to get gallons used, multiply by 4.546 to convert to litres, then multiply by the price per litre. For example: 200 miles at 40 MPG = 5 gallons = 22.7 litres. At £1.45/L that costs £32.95.

What MPG should I use?

Use your real-world MPG, not the manufacturer figure. Check your trip computer or calculate from your last fill-up. Real-world MPG is typically 15-20% lower than the official figure. Motorway driving usually gives better MPG than city driving.

Is driving cheaper than the train?

For a single occupant, trains are often comparable or cheaper for long journeys booked in advance. With 2+ passengers sharing fuel costs, driving is usually significantly cheaper. The comparison here uses average UK rail fares of about £0.15 per mile per person.

How much CO2 does a car journey produce?

A typical petrol car produces about 2.31 kg of CO2 per litre of fuel burned (diesel is slightly higher at 2.68 kg). A 200-mile trip at 40 MPG produces roughly 52 kg of CO2. Train travel typically produces about 40% less CO2 per passenger mile.

CarCalcs

Trip Fuel Cost Calculator

Calculate the fuel cost for a specific journey including cost per person and CO2 emissions.

Trip Distance

Distance to calculate for

Fuel Price

Current price of fuel

Vehicle MPG

Your fuel economy in miles per gallon

Passengers

Return trip (double distance)

Distance to calculate for

How We Calculate This

The calculator works out fuel consumption and costs step by step:

Fuel needed = Distance / MPG (gives gallons) x 4.546 (converts to litres)
Total cost = Fuel litres x price per litre
Cost per person = Total cost / number of passengers
CO2 = Fuel litres x 2.31 kg (petrol emission factor)

Advanced options adjust MPG for city/motorway driving mix and cold start efficiency losses.

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Actual figures may vary based on driving conditions, vehicle specifications, and other factors.