Miles per gallon

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Miles per gallon (MPG) is a unit of measurement that measures fuel economy in automobiles, that is, how many miles a vehicle can travel on one gallon of fuel. It is used similarly in North America and the United Kingdom, although the U.S. gallon is about 83% of the Imperial gallon used in the UK.

Conversion to SI units

MPG to L/100km conversion chart: blue=liq.gal.(US), red=imp.gal.(UK)

Most countries other than the US and UK use the metric units litre (approximately 0.220 Imperial gallons or 0.264 US liquid gallons) and km (approximately 0.621 statute miles). These can be combined to either km/l (efficiency) or l/100 km (consumption). The UK is a special case in this respect, as distances are measured in miles but fuel is sold by the litre. As a result, both MPG and l/100 km are usually quoted for any given vehicle. The general public in the Anglo-Saxon countries, except Australia, almost exclusively use miles-per-gallon. People in the rest of the world prefer l/100 km. Note that because the imperial gallon is significantly larger than the U.S. gallon, MPG figures are 20.095% higher in the UK than in the U.S. for the same real fuel economy.

US liquid gallons

• 1 MPG ≈ 0.425 km/l
• 235/MPG ≈ l/100 km
• 1 MPG ≈ 1.201 MPG (Imp)

Imperial gallons (UK)

• 1 MPG ≈ 0.354 km/l
• 282/MPG ≈ l/100 km
• 1 MPG ≈ 0.833 MPG (US)

Increase in MPG and decrease in l/100 km

One should note that MPG works differently than litres per hundred kilometres. l/100 km denotes a rate of fuel consumption, while MPG is a measure of fuel economy (or 'gas mileage'). If a car uses less fuel, the MPG increases, and l/100 km decreases, but the percentages will not match, because the values are reciprocal.

For example, 20% better mileage does not mean 20%, but 16.7% less fuel. This comes from the following calculation: 20% is 1.2 times bigger distance, therefore 100% / 1.2 = 83.3% of the original fuel consumption, or 16.7% less fuel.

Because consumption is an inverse function of MPG, MPG can be a misleading indicator of fuel efficiency gains. People intuitively take the difference in MPG when comparing two cars. This leads them to underestimate the savings from small improvements on low MPG cars (e.g., 14 to 20 MPG, which saves twice as much fuel over a given distance as the improvement from 33 to 50 MPG ^[1]). A measure of "Gallons Per Mile" (GPM), such as gallons per 100 miles, provides an accurate view of consumption for a given distance of driving. Unlike MPG, the GPM of one car can be subtracted from the GPM of another car to get a direct measure of fuel savings.

Conversion Tables

The conversion tables give a quick overview of the relationship between the different measurement units, MPG (U.S.), MPG (Imperial), km/l, and l/100 km.

Conversion from MPG

Conversion from km/l and l/100 km

See also

• Miles Per Gallon Calculator
• Cost-per-mile
• Dynamometer
• Gallons Per Mile
• Gasoline gallon equivalent
• Miles per gallon gasoline equivalent (MPGGE)
• Vehicle metrics
• Wh/mi and MJ/km

References

1. ^ http://www.mpgillusion.com www.mpgillusion.com