MPG to L/100km Fuel Economy Converter
Convert fuel economy between MPG (US), MPG (UK), liters per 100 km and km/L. Enter any value, choose its unit, and get all four equivalents at once.
Convert Fuel Economy Units
Fuel Economy Converter Formula
Where:
- \(V_{\text{MPG US}}\) — the value expressed in miles per US gallon
- \(V_{\text{MPG UK}}\) — the value expressed in miles per UK (imperial) gallon
- \(V_{\text{km/L}}\) — the value expressed in kilometers per liter
- \(V_{\text{L/100 km}}\) — the value expressed in liters per 100 km
The calculator converts every input first into L/100km (the common base unit) and then derives the other three units from it. The constants follow from the exact definitions of the units: 1 US gallon = 3.785411784 L, 1 UK gallon = 4.54609 L, and 1 mile = 1.609344 km, so \(235.214583 = 100 \times 3.785411784 / 1.609344\) and \(282.480936 = 100 \times 4.54609 / 1.609344\).
Fuel Economy Converter – Calculation Example
Example: a car is rated at 25 miles per US gallon. Convert this rating into the other three units.
\[ \text{L/100 km} = \frac{235.214583}{25} = 9.41 \]
\[ \text{km/L} = \frac{100}{9.4086} = 10.63 \]
\[ \text{MPG UK} = \frac{282.480936}{9.4086} = 30.02 \]
Result: 25 MPG (US) = 9.41 L/100 km = 10.63 km/L = 30.02 MPG (UK).
How to Use the Calculator
- Type your number into the Fuel economy value field (it must be greater than 0).
- Select the unit this value is currently in from the From unit dropdown: Miles per US gallon (MPG US), Miles per UK gallon (MPG UK), Liters per 100 km (L/100km), or Kilometers per liter (km/L).
- Read the results under Equivalent Fuel Economy: the same fuel economy shown in all four units, rounded to two decimals.
- Change the value or the unit at any time — all four results update instantly.
What These Fuel Economy Units Mean
Fuel economy is expressed in two opposite ways. Miles per gallon (MPG) and kilometers per liter (km/L) are distance per fuel units: how far you can drive on one gallon or one liter. Higher values mean better efficiency. Liters per 100 km (L/100km) is a fuel per distance unit: how much fuel you burn to cover 100 km. Here, lower values mean better efficiency. Because the two families run in opposite directions, you cannot compare them by eye — a car that uses half the fuel doubles its MPG but halves its L/100km.
The US and UK gallons are different volumes: the imperial gallon is 4.54609 L while the US gallon is only 3.785411784 L — about 20% smaller. This is why the same real-world efficiency gives noticeably different numbers: 25 MPG (US) equals 30.02 MPG (UK). Confusing the two gallons is one of the most common mistakes when comparing vehicles advertised in different countries, which is why this calculator keeps them separate.
The L/100km scale has a practical advantage: fuel consumed — and therefore fuel cost — is directly proportional to it. A car at 9 L/100km uses exactly three times as much fuel over a given distance as one at 3 L/100km. On the MPG scale the same comparison requires division, because the relationship is inverse.
Quick Reference Table
| MPG (US) | L/100 km | km/L | MPG (UK) |
|---|---|---|---|
| 10 | 23.52 | 4.25 | 12.00 |
| 20 | 11.76 | 8.50 | 24.02 |
| 25 | 9.41 | 10.63 | 30.02 |
| 30 | 7.84 | 12.75 | 36.03 |
| 40 | 5.88 | 17.00 | 48.04 |
| 50 | 4.70 | 21.26 | 60.05 |
Assumptions, Limitations and Tips
- The calculator uses exact legal definitions of the units (1 mile = 1.609344 km, 1 US gal = 3.785411784 L, 1 UK gal = 4.54609 L), so results are accurate to the precision shown.
- The input value must be greater than 0. A rating of 0 MPG or 0 km/L would correspond to infinite consumption and cannot be converted.
- Official fuel economy ratings (city, highway, combined) are measured under standardized test conditions; your real-world consumption will usually be somewhat higher. Convert the rating you actually want to compare, not a rough guess.
- When comparing cars from different markets, always check which gallon the figure uses. Advertised "MPG" in the United States is MPG US; in the United Kingdom and Canada it is MPG UK.
- If you are planning a trip, remember that fuel cost scales linearly with L/100km: multiply the L/100km figure by the distance in hundreds of km and by the price per liter.
For related conversions while comparing vehicles or planning a drive, you may also find the Speed Converter useful for switching between km/h and mph, and the Volume Table for converting between gallons, liters and other volume units. If you need to convert distances themselves, try the Meters to Feet converter.
Frequently Asked Questions
What's the difference between km/L and L/100km?
They are reciprocals scaled by 100: \( \text{km/L} = 100 / \text{L/100km} \). Km/L (like MPG) is distance per unit of fuel, so higher is better; L/100km is fuel per distance, so lower is better. Japan, India and several other countries commonly use km/L, while most of Europe and Australia use L/100km. A car doing 15 km/L uses 6.67 L/100km.