Fuel economy converter
Convert mpg to L/100km, US mpg to UK mpg and km/L, with the reciprocal relationship handled correctly instead of a naive multiply.
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30 mpg (US) = 7.84048611111 L/100 km
Automatic formatting keeps up to 12 significant digits and switches to scientific notation only for numbers past 10¹⁸ or below 10⁻⁹. You can paste values with thousands separators, and fractions such as 3/4 or 1 1/2 are understood too.
L/100 km = 235.214583333 ÷ mpg (US)
Your value: 235.214583333 ÷ 30 = 7.84048611111 L/100 km
Miles per gallon (US): The US gallon is 3.785411784 L, so US mpg reads about 17 % lower than the same car’s UK mpg.
Litres per 100 km: Europe, Canada, Australia, China. A consumption figure: it goes down as the car gets more efficient.
- mpg (US) → L/100 km1 = 235.214583333
- L/100 km → mpg (US)1 = 235.214583333
- mpg (UK) → L/100 km1 = 282.48093628
- L/100 km → mpg (UK)1 = 282.48093628
- mpg (US) → mpg (UK)1 = 1.20094992528
- mpg (UK) → mpg (US)1 = 0.832674184783
- km/L → L/100 km1 = 100
- L/100 km → km/L1 = 100
- mpg (US) → km/L1 = 0.42514370743
- km/L → mpg (US)1 = 2.35214583333
- mpg (UK) → km/L1 = 0.35400619
- L/100 km → kWh/100 km1 = 8.9
| mpg (US) | L/100 km |
|---|---|
| 5 | 47.0429166667 |
| 6 | 39.2024305556 |
| 7 | 33.6020833333 |
| 8 | 29.4018229167 |
| 10 | 23.5214583333 |
| 12 | 19.6012152778 |
| 15 | 15.6809722222 |
| 20 | 11.7607291667 |
| 25 | 9.40858333333 |
| 30 | 7.84048611111 |
| 40 | 5.88036458333 |
| 50 | 4.70429166667 |
| L/100 km | mpg (US) |
|---|---|
| 5 | 47.0429166667 |
| 6 | 39.2024305556 |
| 7 | 33.6020833333 |
| 8 | 29.4018229167 |
| 10 | 23.5214583333 |
| 12 | 19.6012152778 |
| 15 | 15.6809722222 |
| 20 | 11.7607291667 |
| 25 | 9.40858333333 |
| 30 | 7.84048611111 |
| 40 | 5.88036458333 |
| 50 | 4.70429166667 |
| Unit | Symbol | Value in L/100 km | Notes |
|---|---|---|---|
| Litres per 100 kmConsumption (lower is better) | L/100 km | 1 L/100 km = 1 L/100 km | Europe, Canada, Australia, China. A consumption figure: it goes down as the car gets more efficient. |
| Litres per 100 milesConsumption (lower is better) | L/100 mi | 1 L/100 mi = 0.621371192237 L/100 km | Occasionally used in the UK. |
| Miles per gallon (US)Economy (higher is better) | mpg (US) | 1 mpg (US) = 235.214583333 L/100 km | The US gallon is 3.785411784 L, so US mpg reads about 17 % lower than the same car’s UK mpg. |
| Miles per gallon (imperial/UK)Economy (higher is better) | mpg (UK) | 1 mpg (UK) = 282.48093628 L/100 km | The imperial gallon is 4.54609 L — 20 % bigger than the US one. |
| Kilometres per litreEconomy (higher is better) | km/L | 1 km/L = 100 L/100 km | Japan, India, Brazil and much of Asia. |
| Miles per litreEconomy (higher is better) | mi/L | 1 mi/L = 62.1371192237 L/100 km | — |
| kWh per 100 km (EV equivalent)Electric | kWh/100 km | 1 kWh/100 km = 0.112359550562 L/100 km | Using the US EPA figure that 1 US gallon of petrol ≈ 33.7 kWh, so 1 L ≈ 8.9 kWh. An energy-equivalence figure, not a measurement of the same fuel. |
How to convert fuel economy
- Type your figure into either field. The tool handles the reciprocal relationship for you, so you never have to remember which way round the division goes.
- Pick the units, and watch the group labels: the first group counts fuel per distance (lower is better) and the second counts distance per fuel (higher is better).
- Check the formula panel — it shows the division, not a multiplication, which is the whole reason this conversion trips people up.
Why this conversion is not a multiplication
Miles per gallon and litres per 100 km measure the same thing in opposite directions. One is distance divided by fuel; the other is fuel divided by distance. Converting between them means taking a reciprocal, so the relationship is:
L/100 km = 235.214583 ÷ mpg (US), and mpg (US) = 235.214583 ÷ L/100 km.
For imperial gallons the constant is 282.480936. The number itself is just 100 litres per gallon per kilometre per mile, worked out from exact definitions: 3.785411784 L per US gallon and 1.609344 km per mile.
The practical consequence is that improvements are not linear. Going from 15 to 20 mpg saves 1.67 gallons per 100 miles; going from 40 to 45 mpg saves only 0.28 gallons over the same distance. Replacing the thirstiest vehicle in a fleet saves far more fuel than making an already-efficient one slightly better, and the L/100 km scale makes that obvious in a way mpg hides.
US mpg and UK mpg are different numbers
The imperial gallon is 4.54609 litres; the US gallon is 3.785411784. The UK gallon is 20 % larger, so the same car scores about 20 % more miles per gallon on UK figures. A car advertised at 40 mpg in Britain is a 33 mpg car in America. Neither figure is wrong; they simply use different gallons.
| L/100 km | mpg (US) | mpg (UK) | km/L |
|---|---|---|---|
| 4 | 58.8 | 70.6 | 25.0 |
| 5 | 47.0 | 56.5 | 20.0 |
| 6 | 39.2 | 47.1 | 16.7 |
| 7 | 33.6 | 40.4 | 14.3 |
| 8 | 29.4 | 35.3 | 12.5 |
| 10 | 23.5 | 28.2 | 10.0 |
| 12 | 19.6 | 23.5 | 8.3 |
| 15 | 15.7 | 18.8 | 6.7 |
What counts as good
- Under 5 L/100 km (over 47 US mpg): excellent — small diesels and full hybrids.
- 5 to 8 L/100 km: typical for a modern petrol family car driven sensibly.
- 8 to 12 L/100 km: larger petrol cars, SUVs, or mostly short urban trips.
- Over 12 L/100 km (under 20 US mpg): thirsty — big engines, towing, or heavy city driving.
Manufacturer figures come from standardised test cycles (WLTP in Europe, EPA in the US) and real-world consumption typically runs 10 to 25 % higher. The honest way to know your own number is to fill the tank, reset the trip meter, and divide at the next fill.
Electric cars and the kWh option
Electric vehicles are rated in kWh per 100 km, or in miles per kWh in the US. This converter includes a kWh/100 km unit that maps onto the fuel scale using the EPA's equivalence of about 33.7 kWh per US gallon of petrol, which works out at roughly 8.9 kWh per litre. That lets you put an EV and a petrol car on the same axis for an energy comparison.
Treat it as exactly that — an energy comparison, not a fuel one. An EV using 18 kWh/100 km is not "doing 2 L/100 km" in any physical sense; it is using the energy equivalent of two litres of petrol, while an internal combustion engine wastes most of that energy as heat. For running costs, compare the price of a kWh with the price of a litre directly.
Questions
Why can I not just multiply mpg by a number to get L/100km?
Because they run in opposite directions: mpg is distance per fuel, L/100km is fuel per distance. The conversion is a division — L/100km = 235.21 ÷ mpg (US).
Why is UK mpg higher than US mpg for the same car?
The imperial gallon is 4.546 L against the US gallon’s 3.785 L — 20 % more fuel per gallon, so the same car scores about 20 % more miles per gallon on UK figures.
What counts as good fuel economy?
Roughly: under 5 L/100km (47 US mpg) is excellent, 6–8 L/100km is typical for a modern petrol car, and over 12 L/100km (under 20 mpg) is thirsty.
Does the kWh/100 km option work for electric cars?
It converts using the EPA equivalence of about 8.9 kWh per litre of petrol, so it compares energy, not fuel. It is useful for running-cost sums, not for tank size.