Fuel economy guides

Longer reads on the questions the converters raise: why two gallons exist, what the official test figures actually measure, why nobody matches them, and how to measure your own. Written by Aurangzeb Khan, with every constant checked against its primary source.

Guide 1 · 7 min · 1,479 words
US vs UK Gallon: Why the Same MPG Means Different Things
The imperial gallon is 4.54609 litres, the US gallon 3.785411784: a 20.095% gap that changes every mpg figure. Where the two came from and how to convert.
Guide 2 · 7 min · 1,394 words
Understanding Fuel Economy Ratings: EPA, WLTP, NEDC and What They Measure
What the EPA, WLTP, NEDC, WLTC and ARAI fuel economy tests actually measure, why their figures differ for the same car, and how to compare one with another.
Guide 3 · 6 min · 1,171 words
MPG or L/100km: Why Two Systems Exist and Which Is Clearer
MPG measures distance per fuel, L/100km fuel per distance. They are reciprocals, which changes how car comparisons look. Why both exist and which one is honest.
Guide 4 · 6 min · 1,119 words
How to Calculate Your Real Fuel Economy by Hand
The fill-to-fill method for measuring real fuel economy: what to record, the sums in mpg, L/100km and km/L, and the mistakes that make a result meaningless.
Guide 5 · 6 min · 1,120 words
What Counts as Good Fuel Economy in 2026
Realistic 2026 fuel economy benchmarks by type of car, in mpg (US and UK), L/100km and km/L, with the test behind each figure explained so you can judge any number.
Guide 6 · 6 min · 1,127 words
Why Your Real-World MPG Never Matches the Official Figure
Official mpg comes from a lab cycle; your driving does not. The size of the gap, what causes it, which cars fall furthest short, and how to predict your own figure.
Guide 7 · 7 min · 1,268 words
How to Improve Your Fuel Economy
Ways to improve fuel economy ranked by how much each saves: driving style, speed, trip planning, weight, roof racks, idling and maintenance. Numbers, no gadgets.
Guide 8 · 6 min · 1,255 words
How Many Miles Will a Gallon of Gas Get You?
A gallon of gas takes a typical car 20 to 35 miles, a hybrid 50 or more, a pickup under 20. Figures by type of car, how to work out yours, and the metric view.