Mileage Calculator (Bike & Car km/L)

About the Mileage Calculator (Bike & Car km/L)

Find the mileage your bike, scooter or car really gets. Fill the tank to full, note the odometer, ride or drive as usual, then fill to full again: the fuel the tank takes is the fuel you used, and the distance between the two readings divided by it is your mileage. Enter the two readings (or the trip meter) and the litres, and you get km/L, L/100 km and mpg (US and UK) — plus the cost per km, the range on a full tank and your monthly fuel bill if you add the price.

Keep a fill-up log to follow your mileage over time: add each fill-up with its odometer reading, and the tool measures every full tank (adding any partial fills in between), shows the average, best, worst and last tank, a trend chart, the fuel cost per km and what you spend a month. It handles petrol, diesel and CNG (km/kg), km or miles, litres or gallons, several vehicles, and saves everything in your browser.

Common uses

• Checking the real mileage of a new bike or car against the figure in the brochure.
• Spotting a problem early — a sudden drop can mean low tyre pressure, a dragging brake or a service due.
• Knowing your fuel cost per km and monthly fuel spend for budgeting or reimbursement.
• Comparing petrol and CNG running costs, or two vehicles in the same household.

The full-tank (tank-to-tank) method

The US Department of Energy’s fueleconomy.gov describes it as the odometer method: fill the tank completely and write down the odometer; at the next fill-up, fill completely again and note how much fuel it took; subtract the readings and divide the distance by that fuel. The trip meter method is the same with the trip meter reset at the first fill.

It works because the tank is full at both ends, so the fuel added at the second fill is exactly what the engine burned. The pump nozzle does not always click off at precisely the same level, so one tank can be a little high or low — the average over several tanks in the log is the figure to trust.

Partial and missed fill-ups in the log

• Partial fill (not to full): its fuel is added to the next full tank, and the distance runs from the previous full tank. Example: full at 10,000 km, 10 L at 10,400, then 25 L to full at 10,900 gives 900 km ÷ 35 L = 25.7 km/L.
• Missed fill-up: tick I missed logging a fill-up before this one and that stretch is left out (its fuel is unknown); measuring starts again at the next full tank.
• The average is the total distance divided by the total fuel of all measured stretches, so a long highway tank counts more than a short one — the same as one big tank-to-tank measurement.
• Spending: “Average a month” spreads everything paid after your first fill-up over the days up to the last one (30.44 days a month); the monthly table shows what you paid at the pump in each calendar month.

Units and conversions

Exact definitions from NIST (SP 811, App. B.9 and Handbook 44 (2026), App. C): 1 mile = 1.609344 km, 1 UK gallon = 4.54609 L, and 1 US gallon = 231 cubic inches = 3.785411784 L. So L/100 km = 100 ÷ km/L, mpg (US) = km/L × 2.352146 and mpg (UK) = km/L × 2.824809: 40 km/L is 2.5 L/100 km, 94.1 mpg (US) or 113 mpg (UK). For CNG, mileage is in km per kg.

Limitations

• One tank is only as accurate as the two fill levels; for a reliable figure, log several full tanks.
• The result is only as accurate as the odometer, which can be off — for example after fitting tyres of a different size.
• Electric vehicles are not covered: their range and kWh use are best read from the vehicle or the charger.
• The log is saved in this browser only (up to 1,000 fill-ups per vehicle, 10 vehicles); download the CSV to keep a backup.

Privacy

Everything happens in your browser. Your readings and fill-up log are stored in this browser only and are never uploaded; the CSV download is made on your device.