Fuel Economy Converter

Last updated: 2026-05-18

Four Units, One Measurement

Fuel economy — how far a vehicle travels on a given amount of fuel — is expressed in four common units worldwide, and they are not all equivalent:

Unit	Used In	Better =
L/100km	Europe, Korea, Middle East	Lower
MPG (US)	United States, Canada	Higher
MPG (UK)	United Kingdom	Higher
km/L	Japan, Brazil, Southeast Asia	Higher

This fragmentation creates genuine confusion when comparing a Japanese car's stated efficiency (km/L) with a European figure (L/100km) or an American rating (MPG US).

The Reciprocal Relationship

L/100km and km/L are exact reciprocals: one measures fuel per distance, the other measures distance per fuel. To convert between them:

$$\text{km/L} = \frac{100}{\text{L/100km}}$$ $$\text{L/100km} = \frac{100}{\text{km/L}}$$

A car that gets 10 L/100km also gets exactly 10 km/L — the numbers happen to be the same in this example, but they measure the same efficiency from opposite perspectives.

MPG (US and UK) also share this reciprocal relationship with L/100km, using the gallon size as the connecting factor.

US Gallon vs UK Gallon

The single most common source of confusion is that "MPG" means different things in the US and UK:

Gallon	Volume	Conversion Factor
US gallon	3.785 L	1 L/100km = 235.215 MPG(US)
UK (Imperial) gallon	4.546 L	1 L/100km = 282.481 MPG(UK)

Because a UK gallon holds about 20% more fuel than a US gallon, the same vehicle will always have a numerically higher UK MPG figure than US MPG. A car rated at 30 MPG (US) is approximately 36 MPG (UK) — the car has not become more efficient, only the unit of measurement changed.

Rule of thumb: multiply US MPG by 1.201 to get UK MPG.

Conversion Formulas

All conversions pass through L/100km as a common base:

$$\text{MPG (US)} = \frac{235.215}{\text{L/100km}}$$ $$\text{MPG (UK)} = \frac{282.481}{\text{L/100km}}$$ $$\text{km/L} = \frac{100}{\text{L/100km}}$$

The constants 235.215 and 282.481 come from combining the mile-to-kilometre ratio (1 mile = 1.60934 km) with each gallon's litre equivalent.

Which Direction Is "Better"?

Unit	More Fuel-Efficient =
L/100km	Lower number (less fuel burned per 100 km)
MPG (US or UK)	Higher number (more miles per gallon)
km/L	Higher number (more km per litre)

A common mistake is assuming a bigger number is always better. If someone says their car does 5, you need to know the unit: 5 L/100km is excellent efficiency, while 5 MPG is an extremely poor rating (typical for large trucks towing heavy loads).

Typical Values for Passenger Cars

Vehicle Type	L/100km	MPG (US)	km/L
Fuel-efficient compact	4–6	39–59	17–25
Average sedan	7–10	24–34	10–14
SUV / crossover	10–14	17–24	7–10
Large truck or van	14–20	12–17	5–7
Hybrid (e.g. Toyota Prius)	~4.5	~52	~22

Electric Vehicles

Electric vehicles do not use litres or gallons, so fuel economy converters do not apply directly. Instead, EVs are rated in:

• kWh/100km (Europe, similar logic to L/100km — lower is better)
• MPGe (US — miles per gallon equivalent, an energy-equivalent conversion)
• km/kWh (Japan, similar to km/L — higher is better)

If you are comparing a petrol car to an EV, you need an energy-equivalence calculation rather than a simple unit conversion.

Frequently Asked Questions (FAQ)

How do I convert MPG to L/100km?

Divide 235.215 by your MPG (US) value to get L/100km. For example, 235.215 ÷ 30 MPG (US) ≈ 7.84 L/100km. For UK MPG, divide 282.481 by your value instead. The division is necessary because the units are reciprocals of each other — higher MPG corresponds to lower L/100km.

Why is UK MPG always higher than US MPG for the same car?

A UK (Imperial) gallon is larger than a US gallon: 4.546 L vs. 3.785 L. So the same car travels more miles before running out of a UK gallon than a US gallon. The conversion factor is approximately 1.201 — multiply US MPG by 1.201 to get UK MPG. A car rated 30 MPG (US) is approximately 36 MPG (UK).

Why does a lower L/100km number mean better fuel economy?

L/100km measures how much fuel you burn per 100 km of driving. A lower number means you use less fuel for the same distance, which is more efficient. This is opposite to MPG and km/L, where higher numbers indicate better efficiency. Think of it like a grocery bill: a lower price per item is better.

How do I convert km/L to MPG?

To convert km/L to US MPG, multiply by 2.3521 (or equivalently, divide 235.215 by (100 / km/L)). For example, 15 km/L × 2.3521 ≈ 35.3 MPG (US). Alternatively, convert km/L to L/100km first by dividing 100 by your km/L value, then use the L/100km converter above.