HSC · Topic explainer

Converting miles per gallon to litres per 100 km

Convert the distance travelled on one gallon to kilometres and the gallon volume to litres. Divide litres by kilometres, then multiply by 100. The direction of the ratio changes because miles per gallon measures distance per fuel volume and litres per 100 km measures fuel volume per distance.

Worked example

Using the supplied approximations 1 mile = 1.6 km and 1 US gallon = 3.8 L, a car that gets 25 US mpg travels 40 km on 3.8 L.

Divide 3.8 by 40 to obtain 0.095 L/km. Multiply by 100 to get 9.5 L/100 km. Use the conversion given for the gallon in the question because US and imperial gallons have different volumes.

25 miles on one US gallon. 40 km on 3.8 L. 3.8 ÷ 40 × 100 = 9.5 L/100 km.

Official exam practice

2025 HSC Mathematics Standard 2, Question 38

Find other years and marking guidance in the Mathematics Standard 2 official exam archive.