How to use the fuel cost calculator
- Pick your units — miles/MPG or km with L/100km.
- Enter the distance, your vehicle's efficiency and the current fuel price.
- Tick round trip to double it, and set passengers to split the cost.
Getting an accurate estimate
The maths is simple — fuel needed = distance ÷ efficiency, and cost = fuel × price — but the accuracy depends entirely on your efficiency figure. Manufacturer MPG ratings are usually optimistic; your real-world number from tracking a few tanks is far better. Motorway cruising is typically more efficient than city driving, while heavy loads, roof boxes, air conditioning and high speeds all push consumption up, so add a margin for a loaded holiday trip.
Benefits
- Calculates trip fuel cost from distance, efficiency and price.
- Supports both miles/MPG and km with L/100km.
- Splits the cost per passenger and shows cost per mile or km.
- One-tick round-trip option.
Limitations to know
- Accuracy depends on your efficiency figure, and manufacturer MPG is often optimistic.
- It covers fuel only — not tolls, parking or vehicle wear.
- UK and US gallons differ, so keep your units consistent.
Common mistakes to avoid
- Using the manufacturer MPG instead of your real-world average.
- Mixing a UK-gallon MPG with a US-gallon fuel price.
- Forgetting the round-trip tick when planning a return journey.
Alternatives
To convert distances use the Unit Converter; to split other costs use the Tip Calculator.
Last updated: August 2026 · Reviewed by the AI Toolbox editorial team.
Frequently asked questions
Where do I find my MPG?
Your trip computer shows an average, or divide distance travelled by fuel used over a few full tanks for a real-world figure.
Does it handle L/100km?
Yes — switch to the metric toggle and enter litres per 100 km, the standard European measure.
Are UK and US gallons different?
Yes — a UK gallon is about 20% larger. Make sure your MPG and price use the same gallon.
Does it include tolls or wear?
No — this is fuel only. Add tolls, parking and running costs separately.