Fuel Consumption Converter
Convert fuel economy between mpg (US and UK), L/100km and km/L with the exact formulas and worked steps for any pair.
Fuel Consumption Converter — input your values
What does this conversion calculator do?
The fuel consumption converter works with the four standard fuel economy measures: miles per US gallon, miles per UK (imperial) gallon, liters per 100 kilometers and kilometers per liter.
These units are not linearly related to each other, so the converter does the math directly: it first expresses the input as miles per US gallon and then converts that value to the target unit using the exact formulas. Note that lower L/100km means better economy, while higher mpg means better economy.
Formula and variables
The 235.214583 constant converts US gallons to liters per 100 km. The UK gallon is 1.20095 US gallons.
| Symbol | Meaning |
|---|---|
| mpg(US) | Miles traveled per US gallon consumed |
| mpg(UK) | Miles traveled per imperial (UK) gallon consumed |
| L/100km | Liters consumed per 100 kilometers |
| km/L | Kilometers traveled per liter consumed |
Worked example
Convert 30 mpg (US) into liters per 100 km.
- 30 mpg (US) is already the reference unit.
- 235.214583 ÷ 30 = 7.84049.
Answer: 30 mpg (US) ≈ 7.84 L/100km.
Tips and common mistakes
Tips
- Quick anchors: 7 L/100km ≈ 33.6 mpg (US), and 5 L/100km ≈ 47 mpg (US).
- European and Asian vehicles quote L/100km, while North American and UK cars use mpg — check which before comparing.
- To estimate fuel cost, multiply L/100km by distance in hundreds of km and by the fuel price per liter.
- Remember that 100 ÷ L/100km gives km/L directly, and 235.214 ÷ mpg (US) gives L/100km.
Common mistakes to avoid
- Using the US gallon constant for UK mpg values — the imperial gallon is 1.20095 US gallons, so UK mpg figures are always higher.
- Thinking higher L/100km means better economy — it is the opposite: lower liters per 100 km is more efficient.
- Comparing mpg (UK) and mpg (US) figures directly without conversion — they differ by about 20%.
Fuel Consumption Converter — frequently asked questions
What is the difference between mpg US and mpg UK?
The UK (imperial) gallon is 1.20095 times larger than the US gallon, so for the same vehicle mpg (UK) is about 20% higher. Never compare them directly.
How do I convert L/100km to mpg?
Divide 235.214583 by the L/100km value. For example, 7 L/100km → 235.214583 ÷ 7 ≈ 33.6 mpg (US).
Is a higher mpg better?
Yes — more miles per gallon means less fuel for the same distance. For L/100km it is the opposite: a lower number is better.
What is a good fuel consumption?
For modern cars, roughly 5–7 L/100km (33–47 mpg US) is efficient; SUVs and trucks often use 9–12 L/100km (20–26 mpg US).
How do I calculate km/L from L/100km?
Divide 100 by the L/100km value. A vehicle using 8 L/100km travels 100 ÷ 8 = 12.5 km per liter.
Why does my car's displayed mpg differ from the manual's figure?
Official figures come from standardized tests with idealized conditions. Real-world driving, traffic, load, tires and climate change actual consumption by 10–20%.