Gas Mileage Calculator
Gas mileage is a rate, and it arrives in two scales that run in opposite directions: litres per 100 kilometres, where lower is better, and miles per gallon, where higher is better. Converting between them is a reciprocal, not a single multiplication.
Consumption in litres per 100 kilometres
8
- Consumption in miles per US gallon
- 29.4018
- Fuel cost per kilometre
- 0.132
- Fuel cost per 100 kilometres
- 13.2
Values update as you type. This calculator covers the single scenario its formula assumes — see Common Mistakes for what it leaves out.
The formula this calculator uses
mpg = 100 / (L/100km) x 3.785411784 / 1.609344
- V
- Fuel burned in litres, measured between two full fills
- d
- Distance covered in kilometres, matching the litres
- L/100km
- Consumption — litres per 100 kilometres; lower is better
- mpg
- Consumption — miles per US gallon; higher is better
How to check the result by hand
- 1
Measure over two full fills
Fill the tank to the same point, reset the trip odometer, and record the litres added at the next fill. Those litres are what the distance between the fills actually consumed, which is why a partial fill cannot produce a valid figure and a single fill cannot produce one at all.
- 2
Divide litres by distance, then scale to 100
36 litres over 450 kilometres is 36 / 450 = 0.08 litres per kilometre, and multiplying by 100 gives 8.0 litres per 100 kilometres. The scaling simply expresses the rate over a distance that is easy to compare between trips of different lengths.
- 3
Convert to miles per gallon if you need the other scale
Take the reciprocal and apply both unit conversions: 100 / 8.0 x 3.785411784 / 1.609344 = 29.401822916666664 miles per US gallon. Dividing by the L/100km figure, never multiplying, is what respects the reciprocal relationship between the two scales.
- 4
Turn the litres into money
Multiply the litres burned by the price per litre and divide by distance: 36 x 1.65 / 450 = 0.132 per kilometre, and 13.200000000000001 per 100 kilometres. Keep the price in the same volume unit as the litres you measured, or the total is meaningless even when the arithmetic is correct.
- 5
Sanity-check against the scale you know
A figure near 8.0 litres per 100 kilometres should convert to about 29 miles per gallon, and a figure near 40 miles per gallon should sit near 5.9 litres per 100 kilometres. If the two do not agree in direction, an inversion or the wrong gallon is the likely culprit.
For worked examples, common mistakes and the limits of this formula, read the full How To Calculate Gas Mileage page.