Fuel Consumption Converter
Fuel economy is reported two ways: distance per unit of fuel (miles per gallon, kilometers per liter) and fuel per unit of distance (liters per 100 km). The two forms are reciprocals, so a clean conversion has to invert the value, not just scale it. This converter handles US MPG, imperial (UK) MPG, liters per 100 km, and kilometers per liter, converting between any pair. It uses the exact defined factors (1 mile = 1.609344 km, 1 US gallon = 3.785411784 L, 1 imperial gallon = 4.54609 L) and a common kilometers-per-liter base so every result is consistent.
Fuel economy conversion logic
US MPG to km/L: value * 1.609344 / 3.785411784
UK MPG to km/L: value * 1.609344 / 4.54609
km/L base value, then:
to US MPG: km/L * 3.785411784 / 1.609344
to UK MPG: km/L * 4.54609 / 1.609344
to L/100km: 100 / km/L
Distance-per-fuel units (MPG, km/L) convert by scaling. The fuel-per-distance unit L/100km is the reciprocal of km/L scaled to 100 km, so it is computed by division.
Fuel measurement context
- The US gallon (3.785411784 L) is smaller than the imperial gallon (4.54609 L), so US MPG figures read lower.
- The mile is defined as exactly 1.609344 km internationally.
- L/100km is the standard metric measure in most of the world and is inversely related to MPG.
- Lower L/100km means better economy; higher MPG means better economy.
- The US Environmental Protection Agency publishes official fuel-economy estimates for US vehicles.
Fuel consumption: frequently asked questions
Why is converting MPG to L/100km not a simple multiplication?
Miles per gallon measures distance per unit of fuel, while liters per 100 km measures fuel per unit of distance. They are reciprocals of each other, so converting between the two requires dividing a constant by the value rather than multiplying. That is why doubling MPG does not halve L/100km in a straight line.
What is the difference between US MPG and UK (imperial) MPG?
They use different gallons. The US gallon is 3.785411784 liters; the imperial (UK) gallon is 4.54609 liters. Because the imperial gallon is larger, the same vehicle shows a higher number in UK MPG than in US MPG. This converter keeps the two separate.
Which units does this converter support?
US miles per gallon, imperial (UK) miles per gallon, liters per 100 kilometers, and kilometers per liter. You can convert between any pair, including between distance-per-fuel and fuel-per-distance forms.
What are the exact conversion factors used?
1 mile = 1.609344 km exactly, 1 US gallon = 3.785411784 L exactly, and 1 imperial gallon = 4.54609 L exactly, all defined by NIST and international agreement. The converter reduces every input to kilometers per liter as a common base, then converts out.
How is L/100km handled when economy is zero?
Liters per 100 km is the reciprocal of fuel economy, so a value of zero distance per fuel would correspond to infinite consumption. The converter guards against division by zero and shows n/a rather than an infinite or misleading number.
Official sources
- U.S. Department of Energy and EPA: FuelEconomy.gov.
- NIST Special Publication 811: Guide for the Use of the International System of Units.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.