US MPG vs UK MPG: What Is the Difference?
When reading British automotive publications like Top Gear or Autocar, you may notice vehicles achieving seemingly incredible fuel economy. This difference is caused by the physical volume of the British Imperial gallon.
1 UK Imperial Gallon (4.546 L) contains roughly 20% more fuel than 1 US Gallon (3.785 L).
The Origin of the Gallon Discrepancy
In 1824, the British Parliament standardized the Imperial gallon as the volume of 10 pounds of pure water at 62°F (4.54609 liters).
The United States, having declared independence decades earlier, retained the older Queen Anne wine gallon of 231 cubic inches (3.78541 liters).
Consequently, a gallon in the UK contains 760.68 mL more fuel than a gallon in the US.
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