US gallons per 100 miles fuel economy unit.
US gallons per 100 miles to Miles per imperial gallon Converter — gal/100 mi to mpg imp
Convert US gallons per 100 miles (gal/100 mi) to Miles per imperial gallon (mpg imp) using the exact conversion factor (1 us gallons per 100 miles = 120.0949926 miles per imperial gallon). See the formula, worked examples, conversion table, history, and common uses.
US gallons per 100 miles to Miles per imperial gallon converter
Converter
Fuel Economy Converter
Convert MPG, km/L, L/100 km, and related transport fuel economy units.
Context values
Some unit families need one extra value for a physically accurate result.
Miles per imperial gallon fuel economy unit.
Normalize fuel economy to distance per volume, inverting consumption units when needed.
Fuel economy supports both distance-per-volume and volume-per-distance units.
Reserved above the conversion cards and below the converter.
About Converting US gallons per 100 miles to Miles per imperial gallon
US gallons per 100 miles and Miles per imperial gallon are two of the ways the world measures fuel efficiency, and converting between them is essential for comparing a US car's window-sticker rating to a European or Asian one. Specifically: US gallons per 100 miles fuel economy unit, and miles per imperial gallon fuel economy unit.
Formula
Fuel economy formulas invert between distance-per-volume and volume-per-distance units as needed.
Efficiency-style units (like mpg or km/L) and consumption-style units (like L/100 km) measure the same underlying thing from opposite directions, so converting between the two families requires a reciprocal, not just a multiplication factor.
Simple example
1 gal/100 mi × 6.644364e-14 = 120.0949926 mpg imp
1 us gallons per 100 miles = 120.0949926 miles per imperial gallon.
Real-world example
30 gal/100 mi × 6.644364e-14 = 4.003166418 mpg imp
30 us gallons per 100 miles = 4.003166418 miles per imperial gallon.
Conversion table
| US gallons per 100 miles (gal/100 mi) | Miles per imperial gallon (mpg imp) |
|---|---|
| 10 gal/100 mi | 12.00949926 mpg imp |
| 20 gal/100 mi | 6.004749628 mpg imp |
| 30 gal/100 mi | 4.003166418 mpg imp |
| 40 gal/100 mi | 3.002374814 mpg imp |
| 50 gal/100 mi | 2.401899851 mpg imp |
| 60 gal/100 mi | 2.001583209 mpg imp |
Reverse conversion: Miles per imperial gallon to US gallons per 100 miles
120.0949926 mpg imp × 1.505035e+13 = 0.9999999996 gal/100 mi
120.0949926 miles per imperial gallon = 0.9999999996 us gallons per 100 miles.
Fuel economy formulas invert between distance-per-volume and volume-per-distance units as needed.
For a page dedicated to this direction, see Miles per imperial gallon to US gallons per 100 miles.
Understanding the US gallons per 100 miles (gal/100 mi)
US gallons per 100 miles fuel economy unit.
Understanding the Miles per imperial gallon
Miles per imperial gallon (mpg imp) measures fuel economy. Miles per imperial gallon measures distance per imperial gallon (4.54609 L) — about 20% larger than the US gallon, so an imperial MPG figure is correspondingly higher for the same real efficiency. It is classified as a UK/imperial customary unit.
Where it's used: United Kingdom (historically; UK now also uses L/100km)
US mpg vs. imperial mpg. The identical term 'mpg' means a different amount depending on which gallon is used — an imperial mpg figure is about 20% higher than the equivalent US mpg for the same actual fuel efficiency, a common source of confusion when comparing US and UK/Canadian car specs.
Uses of the Miles per imperial gallon today
- UK vehicle fuel-economy figures (particularly older or enthusiast/import contexts)
- Comparing UK-market vehicle specifications to US ones
History of the Miles per imperial gallon
Imperial MPG follows the same automotive tradition as US MPG but uses Britain's imperial gallon (standardized in 1824), leading to the two systems diverging even though they share identical terminology.
Historical origin. Miles per imperial gallon was not the invention of a single named person; it developed through the process described above.
Miles per imperial gallon — sources
- UK Department for Transport — Vehicle fuel economy — Historical basis for UK mpg reporting.
Reserved between the cards and the FAQ so the page stays balanced.
Frequently asked questions
How many miles per imperial gallon are in 1 us gallons per 100 miles?
1 us gallons per 100 miles equals 120.0949926 miles per imperial gallon, using the exact defined conversion factor rather than an estimate.
How do I convert us gallons per 100 miles to miles per imperial gallon?
Fuel economy units sometimes need inversion rather than simple multiplication — the converter above and the formula section handle this automatically.
How do I convert miles per imperial gallon back to us gallons per 100 miles?
Use the reverse factor: 1 miles per imperial gallon equals 120.0949926 us gallons per 100 miles. You can also use the swap control in the converter above to flip the direction instantly.
What is a us gallons per 100 miles?
US gallons per 100 miles (gal/100 mi) is a unit of fuel economy.
What is a miles per imperial gallon?
Miles per imperial gallon (mpg imp) measures fuel economy. Miles per imperial gallon measures distance per imperial gallon (4.54609 L) — about 20% larger than the US gallon, so an imperial MPG figure is correspondingly higher for the same real efficiency. It is classified as a UK/imperial customary unit.
Is the us gallons per 100 miles to miles per imperial gallon conversion exact?
Yes. Both us gallons per 100 miles and miles per imperial gallon are defined by fixed standards rather than physical artifacts, so the factor of 6.644364e-14 used above is exact to as many digits as you choose to display.
What is the difference between us mpg vs. imperial mpg?
The identical term 'mpg' means a different amount depending on which gallon is used — an imperial mpg figure is about 20% higher than the equivalent US mpg for the same actual fuel efficiency, a common source of confusion when comparing US and UK/Canadian car specs.