MPG Calculator

Fuel economy is one ratio read two ways. In US units it is distance over fuel — miles divided by US gallons — and a higher number is better. In metric units it is fuel over distance — litres burned per 100 kilometres — and a lower number is better. Because one measure divides by fuel and the other divides by distance, converting between them is not a multiplication but a division into a constant: L/100 km = 235.214583 ÷ MPG. That constant is exact arithmetic from the definitions, 100 × 3.785411784 litres per US gallon ÷ 1.609344 kilometres per mile, which is why 30 MPG and 7.84 L/100 km are the same economy stated twice, not two estimates.

The honest way to fill the inputs is the full-to-full method: fill the tank, reset the trip meter, drive, then fill again at the same pump and record how much went in. The second fill is the fuel the measured distance actually consumed. Dashboard readouts are useful but optimistic on many cars, and a single short fill is noisy — a few hundred miles between fills averages out the pump's click-off point and your driving mix. This calculator shows both unit systems whatever you enter, so a figure quoted from a US review can be compared with a European brochure figure directly.

Trip-cost mode prices the same arithmetic: fuel for a distance is distance divided by MPG (or distance × L/100 km ÷ 100 in metric), and cost is fuel multiplied by the price you type in. The price is always yours — pump prices change daily and differ by station, so nothing is stored or fetched, and the result is in whatever currency your price was in.