Fuel is the biggest running cost of most trips, and it is easy to estimate once you know your car’s real-world fuel economy. Driving at a steady 50–60 mph, keeping tyres inflated and removing roof boxes can improve economy by 10–20%.
How to use the Fuel Cost Calculator
- Distance
- Round trip (double the distance)
- Fuel economy given as
- Fuel economy
- Fuel consumption
- Fuel price
- People sharing the cost
Results update as you type, and every field accepts the units shown in its menu.
How it works
Enter the distance, choose whether it is a round trip, give the fuel economy in your preferred unit, the fuel price and the number of people sharing the cost.
Tips
- Use your own measured figures – fuel economy, speed and prices vary a lot with driving style, traffic, load and season.
- Pick the unit in each field’s menu (miles or kilometres, mpg or L/100 km); the calculator converts everything for you.
- Fill up to the brim twice and divide the distance by the fuel added to measure real fuel economy.
- For vehicle modifications, treat results as a starting point and confirm with the parts maker or a professional mechanic.
Common mistakes to avoid
- Mixing US and imperial (UK) gallons – a UK gallon is about 20% bigger.
- Using the advertised fuel economy instead of real-world figures.
- Forgetting tolls, parking and wear and tear when comparing driving with public transport.
Inputs explained
| Field | What to enter |
|---|---|
| Distance | Units: mi, km, m, nmi |
| Round trip (double the distance) | Choose one: No, Yes |
| Fuel economy given as | Choose one: Distance per volume (mpg, km/L), Litres per 100 km |
| Fuel economy | Units: mpg (US), mpg (UK), km/L |
| Fuel consumption | In L/100 km |
| Fuel price | Units: /US gal, /L, /UK gal |
| People sharing the cost | A number |
What each result means
- Trip fuel cost = [Fuel needed]×[Fuel price]
- Cost per person = [Trip fuel cost]÷[People sharing the cost]
- CO₂ emitted (petrol) = [Fuel needed]×2347.697029306865
Example values
How the main result changes when Distance changes and everything else stays at the example values above:
| Distance (mi) | Trip fuel cost |
|---|---|
| 125 | 17.5 |
| 187.5 | 26.25 |
| 250 | 35 |
| 312.5 | 43.75 |
| 375 | 52.5 |
| 500 | 70 |
Formula
Fuel used = distance ÷ fuel economy (or distance × L/100 km ÷ 100)Trip cost = fuel used × fuel priceCost per person = trip cost ÷ peopleWorked example
Inputs — Distance: 250 mi; Round trip (double the distance): No; Fuel economy given as: Distance per volume (mpg, km/L); Fuel economy: 25 mpg (US); Fuel consumption: 8 L/100 km; Fuel price: $3.5 /US gal; People sharing the cost: 1.
Results — Fuel needed = 10 US gal; Trip fuel cost = $35.00; Cost per person = $35.00; Cost per distance = $0.140 /mi; CO₂ emitted (petrol) = 88.9 kg.
Frequently asked questions
How do I calculate fuel cost for a trip?
Divide the distance by your mpg to get gallons, then multiply by the price per gallon. 250 miles at 25 mpg and $3.50/gal costs $35.
How do I convert L/100 km to mpg?
US mpg = 235.21 ÷ L/100 km; UK mpg = 282.48 ÷ L/100 km.
Does speed affect fuel economy?
Yes – above about 55–60 mph aerodynamic drag rises quickly; driving at 75 instead of 60 mph can use 20% more fuel.
What formula does the Fuel Cost Calculator use?
Fuel used = distance ÷ fuel economy (or distance × L/100 km ÷ 100).