Why is mpg UK higher than mpg US for the same car?

An Imperial gallon (UK) is larger than a US gallon: 1 Imperial gallon equals 4.54609 litres while 1 US gallon equals 3.78541 litres. Because the UK gallon is about 20 percent larger, mpg UK will always be about 20 percent higher than mpg US for the same vehicle, even though the actual fuel consumption is identical.

How do I convert L/100km to mpg?

To convert L/100km to mpg US, divide 235.215 by the L/100km figure. To convert to mpg UK, divide 282.481 by the L/100km figure. For example, 7 L/100km equals 235.215 divided by 7 = 33.60 mpg US, or 282.481 divided by 7 = 40.35 mpg UK.

What is a good fuel economy for a car?

A typical modern petrol car achieves around 7 to 9 L/100km (26 to 34 mpg US). Fuel-efficient small cars and hybrids can reach 4 to 6 L/100km (39 to 59 mpg US). Larger SUVs and trucks often consume 10 to 14 L/100km. In New Zealand, fuel economy is generally quoted in L/100km on vehicle fuel economy labels.

Fuel Economy Converter

This fuel economy converter switches between the four units used worldwide to describe how efficiently a vehicle uses fuel: litres per 100 kilometres (L/100km), miles per gallon using the US gallon (mpg US), miles per gallon using the Imperial gallon (mpg UK), and kilometres per litre (km/L). New Zealand and Australia quote fuel economy in L/100km on official vehicle labels, where a lower number means better efficiency. The United States uses mpg US and a higher number means better. The United Kingdom uses mpg Imperial, which always reads about 20 percent higher than the US equivalent for the same car because the Imperial gallon (4.54609 L) is larger than the US gallon (3.78541 L). Some Asian markets use km/L, which is the direct inverse of L/100km. Because L/100km is an inverse relationship to mpg and km/L, the maths involves dividing a constant rather than multiplying: to convert L/100km to mpg US you divide 235.215 by the L/100km figure, and to get km/L you divide 100 by L/100km. You choose a unit, enter a value, and all three other equivalents update instantly. The tool is useful when comparing an imported vehicle spec sheet against a local fuel economy rating, when reading car reviews from different countries, or when shopping for a vehicle across regional markets. Values are for reference only and actual fuel consumption will vary with driving conditions, load, and vehicle condition.

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From unit

Value to convert

33.60

mpg US

L/100km7.00

mpg UK40.35

km/L14.29

How it works

The converter uses L/100km as the internal reference. Inputs in other units are first converted to L/100km: mpg US to L/100km by dividing 235.215 by the mpg value; mpg UK to L/100km by dividing 282.481 by the mpg value; km/L to L/100km by dividing 100 by the km/L value. Outputs are then derived from the L/100km figure by reversing these same relationships. The constants 235.215 and 282.481 arise from the number of litres per 100 km equivalent to 1 mpg in each gallon definition combined with the mile-to-kilometre conversion factor of 1.60934.

Worked example

Starting from 7 L/100km: mpg US = 235.215 divided by 7 = 33.60 mpg; mpg UK = 282.481 divided by 7 = 40.35 mpg; km/L = 100 divided by 7 = 14.29 km/L. These match the default values pre-filled in the converter above.

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