Convert fuel economy between mpg, L/100 km and km/L
Car makers, governments and drivers describe fuel use in different ways, and they are not even measuring the same thing. This fuel economy converter switches between miles per US gallon, miles per imperial (UK) gallon, kilometres per litre, litres per 100 km and US gallons per 100 miles, so you can compare a US review, a UK brochure, an Indian mileage claim and a European test figure on equal terms.
Distance-per-fuel units (mpg, km/L) go up as a car gets more efficient; fuel-per-distance units (L/100 km, gal/100 mi) go down. Converting between the two families is a division, not a multiplication, which is why many quick mental conversions go wrong. The converter handles that reciprocal maths for you and shows the formula used.
How to use the Fuel Economy Converter
- Type the figure you have in the Value box, for example 30 or 6.5.
- Choose its unit in From — make sure you pick US or UK mpg correctly.
- Choose the unit you want in To. The round swap button flips the direction.
- Read the result and formula, such as
L/100 km = 235.214583333 ÷ mpg (US). Adjust Precision and press Copy if needed. - Check the list of every fuel economy unit to see the same car described all five ways, or tap a common conversion such as “30 mpg (US) → L/100 km”.
Fuel Economy Converter features
Reciprocal maths built in
Moving between mpg or km/L and L/100 km divides a constant by your value instead of multiplying, exactly as it should.
US and UK mpg kept apart
An imperial gallon is about 20% bigger than a US gallon, so the same car scores about 20% higher in UK mpg.
Gallons per 100 miles
The consumption unit printed on US fuel economy labels, useful for comparing running costs.
km/L for India and Japan
Convert manufacturer mileage claims in km/L to the units used in international reviews.
Zero-safe
A value of zero is flagged instead of producing an infinite or misleading answer.
Fuel economy formulas
All conversions are built from the exact mile (1.609344 km), US gallon (3.785411784 L) and imperial gallon (4.54609 L). The two key constants are 100 × 3.785411784 ÷ 1.609344 = 235.2146 for US mpg and 100 × 4.54609 ÷ 1.609344 = 282.4809 for UK mpg.
- US mpg to L/100 km: L/100 km = 235.2146 ÷ mpg. So 30 mpg (US) = 7.84 L/100 km.
- UK mpg to L/100 km: L/100 km = 282.4809 ÷ mpg. So 40 mpg (UK) = 7.06 L/100 km.
- km/L to L/100 km: L/100 km = 100 ÷ km/L. So 15 km/L = 6.67 L/100 km.
- km/L to US mpg: mpg = km/L × 2.35215. So 20 km/L = 47.04 mpg (US).
- UK mpg to US mpg: multiply by 0.832674. So 50 mpg (UK) = 41.6 mpg (US).
- US mpg to gallons per 100 miles: gal/100 mi = 100 ÷ mpg. So 25 mpg = 4 gallons per 100 miles.
How different countries quote efficiency
| Country or region | Usual unit | Better economy means |
|---|---|---|
| United States | mpg (US gallon); gal/100 mi on the EPA label | Higher mpg, lower gal/100 mi |
| United Kingdom | mpg (imperial gallon), though fuel is sold in litres | Higher mpg |
| Europe, Australia, Canada, China | L/100 km | Lower number |
| India, Japan | km/L (often called “mileage”) | Higher number |
The mpg trap: why consumption units are easier to compare
Imagine driving 10,000 miles. A 10 mpg truck burns 1,000 gallons and a 20 mpg truck burns 500 — a saving of 500 gallons. Upgrading a 30 mpg car to 40 mpg saves only 83 gallons (333 down to 250). The 10-mpg improvement looks identical in both cases, but the fuel saved is six times bigger at the low end.
Consumption units make this obvious: 10 → 20 mpg is 23.5 → 11.8 L/100 km, while 30 → 40 mpg is 7.8 → 5.9 L/100 km. Fuel used is directly proportional to L/100 km or gal/100 mi, which is why they are the better basis for cost estimates. Plug the result into the fuel cost calculator to turn efficiency into money for a trip.
Common fuel economy conversions
| From | To |
|---|---|
| 10 mpg (US) | 23.52145833 L/100 km |
| 20 mpg (US) | 11.76072917 L/100 km |
| 30 mpg (US) | 7.840486111 L/100 km |
| 40 mpg (US) | 5.880364583 L/100 km |
| 50 mpg (UK) | 5.649618727 L/100 km |
| 5 L/100 km | 47.04291667 mpg (US) |
| 8 L/100 km | 29.40182292 mpg (US) |
| 8 L/100 km | 35.31011704 mpg (UK) |
| 15 km/L | 6.666666667 L/100 km |
| 20 km/L | 47.04291667 mpg (US) |
| 25 km/L | 4 L/100 km |
| 1 mpg (UK) | 0.8326741846 mpg (US) |
Fuel Economy Converter FAQ
How do I convert mpg to L/100 km?
Divide 235.215 by the US mpg figure, or 282.481 by the UK mpg figure. For example, 35 mpg (US) is 235.215 ÷ 35 = 6.72 L/100 km. The fuel economy converter does this automatically.
How do I convert km/L to L/100 km?
Divide 100 by the km/L figure. A car that does 18 km/L uses 100 ÷ 18 = 5.56 L/100 km.
Why is UK mpg higher than US mpg for the same car?
Because the imperial gallon (4.546 L) is about 20% larger than the US gallon (3.785 L), so a car travels further on a UK gallon. 1 mpg (UK) = 0.8327 mpg (US).
Is a higher or lower L/100 km better?
Lower. L/100 km measures how much fuel is used to cover 100 km, so a smaller number means a more efficient vehicle — the opposite of mpg and km/L.
How do I convert km/L to mpg?
Multiply km/L by 2.352 for US mpg, or by 2.825 for UK mpg. For example, 15 km/L is 35.3 mpg (US) or 42.4 mpg (UK).
What does gallons per 100 miles mean?
It is the fuel consumed to drive 100 miles. It is 100 divided by mpg, so 25 mpg equals 4 gallons per 100 miles. Because it rises in step with fuel use, it is easier to compare than mpg.