⛽ Fuel Economy Converter (MPG, L/100km)
By ToolNimba Converters Team · Updated 2026-06-19
Remember: higher MPG and km/L are better, while a lower L/100km is better.
Type in any box and the other three update instantly. Values are rounded for display.
Fuel economy is quoted differently around the world: the United States uses miles per US gallon, the United Kingdom uses miles per Imperial gallon, most of Europe and Asia use litres per 100 kilometres, and some regions use kilometres per litre. This converter lets you move between all four in one place. Type a value into any box and the other three update instantly, so you can compare a car spec sheet, a road-test figure or a fuel log no matter which standard it uses.
What is the Fuel Economy Converter?
Fuel economy can be measured two opposite ways, and mixing them up is the single most common error. Distance-per-fuel measures (MPG and km/L) get bigger when a car is more efficient, because you travel further on the same fuel. Fuel-per-distance measures (L/100km) get smaller when a car is more efficient, because you burn less fuel over the same distance. So a high MPG is good, but a high L/100km is bad. The two are inversely related, which is why you cannot simply add or average them across units.
The other trap is the gallon. A US gallon is about 3.785 litres while an Imperial (UK) gallon is about 4.546 litres, roughly 20 percent larger. Because the UK gallon holds more fuel, the same car always scores a higher number in MPG (UK) than in MPG (US). A car rated at 30 MPG (US) is about 36 MPG (UK), even though nothing about the car has changed. Always check which gallon a figure refers to before comparing two vehicles.
This tool converts through a single internal value in L/100km. From any input it works out the litres burned per 100 km, then expresses that same consumption in every other unit. The key relationships are L/100km = 235.215 divided by MPG (US), L/100km = 282.481 divided by MPG (UK), and km/L = MPG (US) multiplied by 0.425144. Because everything routes through one pivot, the conversions stay consistent in both directions.
When to use it
- Comparing a US car spec quoted in MPG with a European model quoted in L/100km.
- Converting a fuel log kept in km/L into MPG to compare against a manufacturer rating.
- Translating a UK road-test MPG figure into US MPG before buying an imported vehicle.
- Working out the L/100km a rental car will use when you are travelling abroad.
- Checking whether a quoted economy figure uses the US gallon or the larger Imperial gallon.
How to use the Fuel Economy Converter
- Pick the unit you already have a number for (MPG US, MPG UK, L/100km, or km/L).
- Type that value into its box, or tap one of the MPG (US) preset buttons.
- Read the other three boxes, which fill in automatically.
- Check the summary line, which restates all four values together for easy comparison.
Formula & method
Worked examples
A US car is rated at 30 MPG (US) and you want the European equivalent in L/100km and km/L.
- Convert to L/100km: 235.215 ÷ 30 = 7.8405, so about 7.84 L/100km.
- Convert to km/L: 30 × 0.425144 = 12.7543, so about 12.75 km/L.
- Convert to MPG (UK): 30 × 1.20095 = 36.0285, so about 36.03 MPG (UK).
Result: 30 MPG (US) ≈ 7.84 L/100km, 12.75 km/L, and 36.03 MPG (UK).
A European hatchback is listed at 6 L/100km and you want to compare it against US figures.
- Convert to MPG (US): 235.215 ÷ 6 = 39.2025, so about 39.20 MPG (US).
- Convert to MPG (UK): 282.481 ÷ 6 = 47.0802, so about 47.08 MPG (UK).
- Convert to km/L: 100 ÷ 6 = 16.6667, so about 16.67 km/L.
Result: 6 L/100km ≈ 39.20 MPG (US), 47.08 MPG (UK), and 16.67 km/L.
Common fuel economy values across all four units
| MPG (US) | MPG (UK) | L/100km | km/L |
|---|---|---|---|
| 20 | 24.02 | 11.76 | 8.50 |
| 30 | 36.03 | 7.84 | 12.75 |
| 40 | 48.04 | 5.88 | 17.01 |
| 50 | 60.05 | 4.70 | 21.26 |
| 60 | 72.06 | 3.92 | 25.51 |
Conversion factors used by this tool
| From | To | Operation |
|---|---|---|
| MPG (US) | L/100km | divide 235.215 by the MPG value |
| MPG (UK) | L/100km | divide 282.481 by the MPG value |
| MPG (US) | km/L | multiply by 0.425144 |
| MPG (US) | MPG (UK) | multiply by 1.20095 |
| L/100km | km/L | divide 100 by the L/100km value |
Common mistakes to avoid
- Treating MPG and L/100km as if they move the same way. They are inverse measures. A higher MPG means better economy, but a higher L/100km means worse economy. Improving from 8 to 6 L/100km is a gain, not a loss.
- Confusing US gallons with Imperial gallons. The Imperial gallon is about 20 percent larger than the US gallon, so MPG (UK) always reads higher than MPG (US) for the same car. Mixing them makes a vehicle look more efficient than it is.
- Averaging fuel economy across a trip. You cannot simply average two MPG figures to get a trip average, because economy is fuel per distance. Add up the total distance and the total fuel, then divide, or convert to L/100km first.
- Assuming km/L and L/100km are interchangeable units. Both are metric, but one is distance per fuel and the other fuel per distance. Use km/L = 100 divided by L/100km to switch between them rather than guessing.
Glossary
- MPG (US)
- Miles travelled per US gallon (about 3.785 litres) of fuel. Higher is more efficient.
- MPG (UK)
- Miles travelled per Imperial gallon (about 4.546 litres) of fuel, used in the United Kingdom. Higher is more efficient.
- L/100km
- Litres of fuel consumed per 100 kilometres travelled. Lower is more efficient.
- km/L
- Kilometres travelled per litre of fuel. Higher is more efficient.
- Imperial gallon
- The UK gallon, about 4.546 litres, roughly 20 percent larger than the US gallon.
- Inverse relationship
- A link where one value rises as the other falls, as between L/100km and MPG.
Frequently asked questions
How do I convert MPG (US) to L/100km?
Divide 235.215 by the MPG value. For example, 30 MPG (US) equals 235.215 divided by 30, which is about 7.84 L/100km. The conversion is inverse, so a higher MPG always gives a lower L/100km.
Why is MPG (UK) a bigger number than MPG (US) for the same car?
The Imperial gallon used in the UK holds about 4.546 litres while the US gallon holds about 3.785 litres. Because the UK gallon is roughly 20 percent larger, the car travels more miles on one gallon, so the MPG (UK) figure is higher even though the car is identical.
How do I convert L/100km to km/L?
Divide 100 by the L/100km value. For example, 8 L/100km equals 100 divided by 8, which is 12.5 km/L. They are inverse measures of the same consumption, so as one rises the other falls.
Is a higher or lower number better for fuel economy?
It depends on the unit. For MPG (US), MPG (UK) and km/L, higher is better because you travel further on the same fuel. For L/100km, lower is better because you burn less fuel over the same distance.
How accurate are these conversions?
The conversion factors are exact to the values shown (235.215 for MPG US and 282.481 for MPG UK), so the math is precise. Displayed results are rounded to two decimals for readability, which is plenty for comparing vehicles.
What is the difference between km/L and L/100km?
Both are metric, but km/L is distance per fuel (higher is better) while L/100km is fuel per distance (lower is better). They describe the same efficiency from opposite directions, linked by km/L = 100 divided by L/100km.