How to Calculate Fuel Cost for a Trip

Published Apr 17, 2026

Knowing your fuel cost before a journey helps with budgeting, comparing vehicles, and deciding between driving and other transport.

The Basic Formula

Fuel used = Distance ÷ Fuel economy
Fuel cost  = Fuel used × Fuel price

Metric (L/100 km):

Fuel used (litres) = Distance (km) × Consumption (L/100 km) ÷ 100
Cost = Fuel used × Price per litre

Imperial (mpg):

Fuel used (gallons) = Distance (miles) ÷ MPG
Cost = Fuel used × Price per gallon

Example 1 (metric): 350 km trip, car uses 7.5 L/100 km, fuel costs £1.55/litre:

Fuel used = 350 × 7.5 ÷ 100 = 26.25 litres
Cost = 26.25 × 1.55 = £40.69

Example 2 (imperial): 200-mile trip, 35 mpg car, fuel costs £1.65/litre (≈ £7.50/UK gallon):

Fuel used = 200 ÷ 35 = 5.71 gallons
Cost = 5.71 × 7.50 = £42.86

Example: 40 mpg (UK) = 282.48 ÷ 40 = 7.06 L/100 km

EV cost example: 350 km trip, 18 kWh/100 km, home charging at £0.28/kWh:

Energy used = 350 × 18 ÷ 100 = 63 kWh
Cost = 63 × 0.28 = £17.64

EVs cost roughly 50–65% less per mile than petrol at home-charging rates, but the saving narrows significantly with public rapid charging.

Beyond trip costs, calculate annual fuel spend:

Annual spend = (Annual mileage ÷ Fuel economy) × Fuel price × 12

Example: 12,000 miles/year, 40 mpg, £1.55/litre (£7.05/gallon):

Gallons/year = 12,000 ÷ 40 = 300 gallons
Annual spend = 300 × 7.05 = £2,115/year

Maintain correct tyre pressure. Under-inflated tyres increase rolling resistance and can worsen fuel economy by 2–3%.
Drive at steady speeds. Motorway speeds of 65–70 mph are typically more economical than 80+ mph (aerodynamic drag increases as the square of speed).
Remove unnecessary weight. An extra 50 kg reduces fuel economy by roughly 1–2%.
Plan routes to avoid stop-start traffic. Idling consumes fuel at 0 mpg.
Use cruise control. Maintains consistent speed better than most drivers.

Use the Fuel Cost Calculator to estimate your trip cost in any unit combination.