Convert L/100km to MPG

Use 235.2146 to convert any L/100km value to US MPG, and 282.4809 for imperial MPG. A car rated at 10 L/100km consumes 10 liters of fuel per 100 kilometers driven. That same car gets 23.5 miles per US gallon (235.2146 ÷ 10) or 28.2 miles per imperial gallon (282.4809 ÷ 10). The exact numbers come from the volume of each gallon in liters and the number of kilometers in 100 miles. This covers both l/100km to mpg conversions, fuel price per liter to per gallon, and the km/L alternative.

The conversion is a single division. For a car that uses 12.5 L/100km:
US MPG = 235.2146 ÷ 12.5 = 18.8
Imperial MPG = 282.4809 ÷ 12.5 = 22.6

The constants come from the number of milliliters in a gallon divided by the number of kilometers in 10 miles. A US gallon is exactly 3.785411784 liters (NIST Handbook 44 Appendix C / NIST SP 811 Appendix B). An imperial gallon is exactly 4.54609 liters (UK Weights and Measures Act 1985 Schedule 1). One mile is 1.609344 kilometers. Multiplying the gallon volume (in mL) by the number of 10-mile segments in 100 km gives the constant.For the imperial gallon, 4546.09 × (100 / 16.09344) = 28248.0936.

Worked Example: 8 L/100km

8 L/100km is a good fuel economy figure, common in modern sedans.
US MPG = 235.2146 ÷ 8 = 29.4
Imperial MPG = 282.4809 ÷ 8 = 35.3

Worked Example: 15 L/100km

15 L/100km is typical for a large SUV or an older vehicle.
US MPG = 235.2146 ÷ 15 = 15.7
Imperial MPG = 282.4809 ÷ 15 = 18.8

L/100km measures fuel consumed per distance. Lower numbers mean the car needs less fuel to travel 100 km, so you spend less. MPG measures distance travelled per gallon of fuel. Higher numbers mean the car goes farther on the same amount of fuel. The two scales are inverses with a constant factor. A car at 5 L/100km is more efficient than one at 10 L/100km. That same car in US MPG is 47.0, which is higher than 23.5.

Confusion peaks when you compare a 30 MPG (US) car in the US with a 36 MPG (imperial) car in the UK. The fuel economy is not identical; the different gallon sizes produce different numbers. US EPA fueleconomy.gov uses the US gallon for all published MPG ratings. Natural Resources Canada uses L/100km for fuel consumption ratings. The gap between the two MPG scales is roughly 20% because the imperial gallon is 20% larger than the US gallon.

To compare fuel costs between the US (price per gallon) and the UK or Canada (price per liter), multiply the per-liter price by the size of the gallon you need. Use the exact conversion factors: 3.785411784 L per US gallon, 4.54609 L per imperial gallon.

If a station in Canada charges $1.50 CAD per liter, the cost per US gallon is $1.50 × 3.7854 = $5.68 CAD per US gallon. Per imperial gallon, it is $1.50 × 4.5461 = $6.82 CAD per imperial gallon.

If a US station charges $3.80 USD per US gallon, the cost per liter is $3.80 ÷ 3.7854 = $1.00 USD per liter. Per imperial gallon, that same $3.80 per US gallon becomes $3.80 × (4.54609 / 3.78541) = $4.56 USD per imperial gallon.

The common failure is assuming a gallon is a single unit. A UK driver visiting the US sees a price of $3.80 per gallon and thinks it is cheap because the UK price is around £6 per imperial gallon. At 2026 exchange rates, $3.80 per US gallon is cheaper than £6 per imperial gallon, but not by the 40% the raw numbers suggest. The 20% volume difference between the two gallons accounts for part of the gap, and the rest is currency.

Km/L is the metric counterpart to MPG. It measures how many kilometers the car travels on one liter of fuel. To convert L/100km to km/L, divide 100 by the L/100km figure. A car at 10 L/100km does 10 km/L (100 ÷ 10). At 5 L/100km, it does 20 km/L. Higher km/L is better, just like higher MPG.

Km/L is used in some European specifications and in scientific contexts. It avoids the gallon ambiguity entirely. A vehicle that does 12 km/L converts to 28.2 US MPG (12 × 2.352) or 33.9 imperial MPG (12 × 2.825). The constant for US MPG from km/L is 2.352 (3.7854 × 0.6214), and for imperial MPG it is 2.825 (4.5461 × 0.6214).

Natural Resources Canada publishes L/100km ratings because the metric scale is unambiguous. The same vehicle sold in Canada and the US will have different numbers on Canadian and American labels, the Canadian one in L/100km and the US one in MPG (US), but the fuel consumption is identical.

Work backwards from a known MPG figure using the same constants. A car rated at 30 MPG (US) has a L/100km value of 235.2146 ÷ 30 = 7.8 L/100km. The same car in imperial MPG would be 30 imperial MPG, which converts to 282.4809 ÷ 30 = 9.4 L/100km. The 30 MPG (US) car is more efficient than the 30 MPG (imperial) car because the US gallon is smaller, meaning the car used fewer gallons to go the same distance.

This is a check for common errors. If you convert a UK spec of 40 MPG (imperial) using the US constant, you get 235.2146 ÷ 40 = 5.9 L/100km, which is unrealistically good for most cars. The correct conversion is 282.4809 ÷ 40 = 7.1 L/100km. Always state which gallon you are converting from.