How it works
The window sticker and the dashboard read-out both flatter your car. The reliable way to know your real gas mileage is the fill-up method: measure the distance between two full tanks and the fuel it took to refill. This calculator gives the answer in every common unit — miles per gallon (US and UK), kilometres per litre and litres per 100 km — so you can compare with any spec sheet.
km/L = distance (km) ÷ litres used · L/100 km = 100 ÷ km/L mpg (US) = km/L × 2.352 · mpg (UK) = km/L × 2.825Worked example. You drove 500 km on 40 litres: 500 ÷ 40 = 12.5 km/L, or 8.0 L/100 km — 29.4 mpg (US) and 35.3 mpg (UK). With a 60-litre tank your range is about 750 km. Going the other way, a car rated 30 mpg (US) does 12.75 km/L, or 7.84 L/100 km. In miles: 300 miles on 10 US gallons is 30 mpg.
The fill-up method
- Fill the tank until the pump clicks off and reset the trip meter.
- Drive normally until the tank is half empty or lower.
- Fill up again to the click. Note the litres (or gallons) on the receipt and the distance on the trip meter.
- Enter both. Repeat over three tanks and average for the most accurate figure.
Working in miles and gallons? Convert first: miles × 1.609 = km, US gallons × 3.785 = litres. Or use the “convert” mode with your mpg figure.
Typical fuel economy
| Vehicle | mpg (US) | L/100 km |
|---|---|---|
| Small car 1.0–1.6 L | 33 – 42 | 5.5 – 7 |
| Mid-size sedan | 26 – 33 | 7 – 9 |
| Mid-size SUV | 21 – 28 | 8.5 – 11 |
| Full-size SUV or V8 pickup | 12 – 19 | 12.5 – 20 |
| Hybrid | 42 – 58 | 4 – 5.5 |
Figures are rough combined-cycle values; city traffic can be 20–40% worse than highway driving. Diesels usually use 15–25% less fuel than a comparable gasoline engine.
Why did my mileage drop?
- Low tyre pressure — check monthly.
- Air conditioning — can cost 10–20% in hot-weather city driving.
- Speed and hard acceleration — economy falls quickly above about 50 mph (80 km/h).
- Maintenance — a dirty air filter, worn spark plugs or a faulty oxygen sensor.
- Extra weight and roof boxes.
To price a whole trip and split it between passengers, use the gas trip cost calculator; for travel time, the speed, distance and time calculator; and to switch units, km to miles.