MPG to Liters per 100 km
Published July 19, 2026By Samson PG
L/100km = 235.215 ÷ mpg (US). Lower L/100km means better efficiency — the inverse of how MPG reads.
MPG (miles per gallon) rises when a car is more efficient. L/100km (liters per 100 kilometers) falls when efficiency improves. Converting between them is a fixed reciprocal relationship once you know which gallon you mean.
US MPG ↔ L/100km
Using the common constant for US liquid gallons:
L/100km = 235.215 / mpg
mpg = 235.215 / (L/100km)Example: 30 mpg (US) → 235.215 ÷ 30 ≈ **7.84 L/100km**.
Imperial (UK) gallon note
UK gallons are larger. The constant is different (commonly cited near 282.481 for imperial mpg ↔ L/100km). Mixing US and UK mpg without labeling causes large errors.
Quick reference (US mpg)
| MPG (US) | ≈ L/100km |
|---|---|
| 20 | 11.8 |
| 25 | 9.4 |
| 30 | 7.8 |
| 35 | 6.7 |
| 40 | 5.9 |
Which number to use
| Region habit | Prefer |
|---|---|
| U.S. stickers / many U.S. drivers | MPG |
| Europe / much of the world | L/100km |
| Comparing two cars | Convert both to one unit first |
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FAQ
Is city MPG the same as highway?
No — duty cycles differ. EPA or WLTP labels are standardized tests, not your commute.
Why doesn’t my fill-up match the sticker?
Driving style, temperature, load, and fuel quality all move real-world economy.
Can I convert km/L instead?
Yes: km/L = 100 / (L/100km).
Does diesel vs petrol change the formula?
The unit conversion is the same; energy content differs but MPG↔L/100km is still geometric.