How this conversion works
Miles per gallon and kilometers per liter measure distance per amount of fuel: higher is better. Liters per 100 km measures fuel per distance: lower is better. Because they are reciprocals, converting to or from L/100 km divides instead of multiplies.
The converter turns your value into kilometers per liter, then into the target unit. US and Imperial mpg differ because the gallons differ in size.
Formula: L/100 km = 235.214583 ÷ mpg (US) · L/100 km = 282.480936 ÷ mpg (Imperial)
Where this conversion is used
- Comparing car fuel economy between US (mpg), UK (Imperial mpg) and European (L/100 km) figures.
- Estimating trip fuel use from a rating in another unit.
- Reading imported vehicle specifications.
Worked example: 30 mpg (US) to L/100 km
- 30 mpg = 30 × 1.609344 km ÷ 3.785411784 L = 12.7543 km/L.
- Take the reciprocal per 100 km: 100 ÷ 12.7543 = 7.8405 L/100 km.
- Shortcut: 235.214583 ÷ 30 = 7.8405.
Miles per US gallon to liters per 100 km
| Miles per gallon (US) (mpg (US)) | Liters per 100 km (L/100 km) |
|---|---|
| 15 | 15.681 |
| 20 | 11.7607 |
| 25 | 9.4086 |
| 30 | 7.8405 |
| 35 | 6.7204 |
| 40 | 5.8804 |
| 50 | 4.7043 |
Liters per 100 km to miles per Imperial gallon
| Liters per 100 km (L/100 km) | Miles per gallon (Imperial) (mpg (Imp)) |
|---|---|
| 4 | 70.6202 |
| 5 | 56.4962 |
| 6 | 47.0802 |
| 7 | 40.3544 |
| 8 | 35.3101 |
| 10 | 28.2481 |
| 12 | 23.5401 |
Things to watch for
- Zero and negative values are rejected because the reciprocal is undefined.
- Halving L/100 km doubles mpg — the scales are not linear against each other.
Precision and sources
Results are calculated from the definitions above and rounded to 12 significant digits; the converter shows up to eight decimal places and the tables four. Reference: NIST Special Publication 811, Guide for the Use of the International System of Units, Appendix B.
Frequently asked questions
Why does L/100 km go down when mpg goes up?
L/100 km measures fuel used for a fixed distance, while mpg measures distance per fixed fuel. One is the inverse of the other.
Are UK and US mpg the same?
No. A UK figure is about 20% higher for the same car, because the Imperial gallon is larger.