What it does
Maker figures for fuel use are measured in a lab. Your own number depends on traffic, load, tyres and how you drive. This tool takes the odometer and the fuel you add at each fill-up and gives you the real figure: km per litre, litres per 100 km, miles per US gallon and miles per UK gallon, plus what each kilometre costs you.
It works for a car, a two-wheeler or a truck, and for electric vehicles if you choose kWh. To price a planned journey use fuel cost, to keep a log for tax or work use mileage log, and EV vs petrol compares an electric vehicle with a petrol one.
How to use it
- Fill the tank to the click, and write down the odometer. That is your first row, ticked Full.
- Next time, fill to the click again. Add a row with the new odometer, the fuel added and the price per unit, and keep Full ticked.
- If you topped up part way, add that row with Full unticked. Its fuel is counted with the next full fill.
- Read the result. Add more rows to see the trend.
What each setting does
- Distance in and Fuel in: the units your odometer and pump use. All results are shown in the common units as well.
- Tank or battery size and Tank level now: used for the range left, which is the tank level times your average km per litre.
- Keep my log on this device: off by default. When ticked, your rows are stored in this browser only; “Clear saved log” removes them.
Worked example
Odometer 10,000 at a full fill-up. At 10,450 you add 30 L and the tank is full again. That is 450 km on 30 L: 15.00 km/L, which is 6.67 L per 100 km, or about 35.3 miles per US gallon. If the fuel was 1.50 a litre, you paid 0.10 per km.
FAQs
Why do I need a full tank each time? The pump only tells you what was added. When the tank is full at both ends, what was added is exactly what was used.
Why does my figure change a lot? Winter, short trips, roof racks and low tyre pressure all cost fuel. The chart shows whether it is a one-off or a trend.
Can I save the log? Download it as a CSV, or tick the keep box to store it in this browser.
Estimates only; the odometer and pump can each be a little out.
Where the numbers come from
- Full-tank method: distance between two full fill-ups divided by the fuel added at the second one. Conversions: 1 mile = 1.609344 km, 1 US gallon = 3.785411784 L, 1 UK (imperial) gallon = 4.54609 L. Tank sizes are typical round numbers you can change. Drawings are fibub's own.
Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.
Last updated 2026-11-10.