How this calculator works
The calculation estimates annual litres at each MPG using UK imperial gallons, then applies your chosen pump price. Because MPG is not linear in fuel consumption, increasing MPG by 20% does not necessarily reduce litres used by 20%.
For example, 10,000 miles at 35 MPG uses roughly 1,299 litres; at 42 MPG it uses about 1,082 litres. The difference is approximately 216 litres before assigning a money value.
Common questions
Why is a change from 30 to 40 MPG bigger than 50 to 60?
Each additional MPG saves fewer litres as MPG increases; the litres-per-mile conversion is reciprocal.
Can I use this for diesel?
Yes. Enter your actual diesel price and diesel MPG. The volume conversion is identical for petrol and diesel.