Utilix knowledge base
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
Worked Examples
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
Unit Conversions
| Measure | Metric | Imperial |
|---|---|---|
| Fuel economy | L/100 km | mpg (miles per gallon) |
| 1 UK gallon | 4.546 litres | — |
| 1 US gallon | 3.785 litres | — |
| Convert mpg (UK) to L/100km | 282.48 ÷ mpg | — |
| Convert L/100km to mpg (UK) | 282.48 ÷ L/100km | — |
Example: 40 mpg (UK) = 282.48 ÷ 40 = 7.06 L/100 km
Petrol vs Diesel vs EV Cost Comparison
| Fuel type | Efficiency | Typical cost/unit |
|---|---|---|
| Petrol | 10–12 L/100 km | £1.40–£1.60/litre |
| Diesel | 7–9 L/100 km | £1.45–£1.65/litre |
| EV | 15–25 kWh/100 km | £0.25–£0.35/kWh (home charging) |
| EV (public rapid) | 15–25 kWh/100 km | £0.50–£0.90/kWh |
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.
Annual Running Cost
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
Tips for Reducing Fuel Costs
- 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.