Fuel efficiency converter: MPG, L/100km, km/L, and imperial MPG

Convert between MPG (US), MPG (Imperial/UK), L/100km, and km/L at ToolHQ's fuel efficiency converter, with clear explanation of why US and UK MPG differ. Free, no account required.

Fuel efficiency is one of the most confusing unit comparisons in everyday life because the same number can mean very different things depending on the country. A car rated at 30 MPG in the US would be rated at about 36 MPG in the UK, not because the car improved, but because the UK uses a larger gallon. And L/100km runs in the opposite direction: lower is better, while MPG is higher is better.

ToolHQ's fuel efficiency converter handles all four units simultaneously and explains the differences so you understand what you are comparing.

Key Takeaways

• 30 MPG (US) = 36 MPG (UK) = 7.8 L/100km = 12.8 km/L
• US gallon = 3.785 liters; UK gallon = 4.546 liters (20% larger)
• For L/100km: lower number = better fuel economy
• For MPG and km/L: higher number = better fuel economy
• No data is stored or transmitted, all calculations run locally in your browser

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US MPG vs. UK MPG: why they are different

This is the most important distinction in fuel efficiency conversion, and many people miss it.

The US gallon is 3.785 liters. The UK (imperial) gallon is 4.546 liters. This makes the UK gallon about 20% larger than the US gallon. As a result:

• A car that travels 30 miles per US gallon goes 30 miles per 3.785 liters
• The same car in UK terms goes 30 miles per 4.546 liters, which is a higher MPG number: approximately 36 MPG UK

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

This difference causes real confusion when:

• Comparing car specs between US and European/UK publications
• Buying a car originally sold in the UK and checking US fuel economy databases
• Reading fuel economy claims from manufacturers who do not specify which gallon they mean

All calculations run locally in your browser, no data is stored or transmitted.

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How the units work: which direction is "better"

Two of the four units measure distance per volume (higher = more efficient). Two measure volume per distance (lower = more efficient):

Unit	Direction	Interpretation
MPG (US)	Higher is better	Miles traveled per US gallon
MPG (UK)	Higher is better	Miles traveled per imperial gallon
km/L	Higher is better	Kilometers traveled per liter
L/100km	Lower is better	Liters consumed per 100 km

The L/100km inversion is the biggest source of confusion when comparing European and American fuel economy figures. A European driver saying "I get 7 L/100km" is describing good efficiency. That equals about 33.6 MPG (US), a solid rating for a mid-size car.

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Conversion formulas

From	To	Formula
MPG (US) to L/100km	L/100km = 235.215 / MPG	30 MPG (US) = 235.215 / 30 = 7.84 L/100km
L/100km to MPG (US)	MPG = 235.215 / L/100km	8 L/100km = 235.215 / 8 = 29.4 MPG (US)
MPG (UK) to L/100km	L/100km = 282.481 / MPG	36 MPG (UK) = 282.481 / 36 = 7.85 L/100km
MPG (US) to km/L	km/L = MPG x 0.4251	30 MPG x 0.4251 = 12.75 km/L
km/L to L/100km	L/100km = 100 / km/L	12.75 km/L = 100 / 12.75 = 7.84 L/100km
MPG (US) to MPG (UK)	MPG (UK) = MPG (US) x 1.201	30 MPG (US) = 36 MPG (UK)

Where does 235.215 come from? One mile equals 1.60934 km. One US gallon equals 3.78541 liters. So 100 km / (MPG miles x 1.60934 km/mile) x 3.78541 L/gallon = 235.215 / MPG. The 282.481 constant uses the imperial gallon (4.54609 L) instead.

Mini-story 1: Tom was buying a used car and comparing two options online. One listing was for a car advertised at "40 MPG" on a UK motoring website. The other was an American import listed on a US dealer site at "33 MPG." He assumed the UK car was more fuel-efficient. Using ToolHQ's fuel efficiency converter, he converted both to L/100km. The UK car at 40 MPG (UK) was 7.06 L/100km. The US car at 33 MPG (US) was 7.13 L/100km. They were essentially identical; the apparent difference was entirely due to the gallon size difference.

Convert fuel efficiency free at ToolHQ

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How to use the ToolHQ fuel efficiency converter

1. Go to the tool. Navigate to ToolHQ's fuel efficiency converter. No account or sign-up required.
2. Enter your value. Type your fuel efficiency figure in the input field.
3. Select your source unit. Choose MPG (US), MPG (UK), L/100km, or km/L.
4. Read all results. The converter returns equivalents in all other units simultaneously.

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Vehicle efficiency reference table

Vehicle type	L/100km (typical)	MPG (US)	MPG (UK)	km/L
EV (energy equivalent)	2.0-3.0	78-118	94-142	33-50
Hybrid compact	3.5-5.0	47-67	57-80	20-29
Efficient gasoline compact	5.5-7.0	34-43	40-52	14-18
Average midsize sedan	7.0-9.0	26-34	31-40	11-14
Large SUV	9.0-13.0	18-26	22-31	8-11
Light truck / pickup	11.0-15.0	16-21	19-26	7-9

Reference point: The US EPA average for new passenger vehicles has been approximately 7.8 L/100km (30 MPG US) in recent years.

For calculating the actual cost of fuel use based on your efficiency rating, ToolHQ's fuel cost calculator takes your efficiency, distance driven, and fuel price to return total fuel cost.

Mini-story 2: Priya was moving from India to the United States and wanted to understand American car specifications. She was used to thinking of fuel efficiency in km/L (India uses the same metric as km/L). A car she was looking at was rated at 32 MPG combined by the EPA. She entered 32 MPG (US) into ToolHQ's fuel efficiency converter and got 13.6 km/L, which she recognized immediately as a reasonable rating for a mid-size car. The converter also showed 7.35 L/100km and 38.4 MPG (UK), giving her a complete picture of how to translate the American EPA rating into terms she was used to.

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Frequently asked questions

Why does the same car get different MPG in the US vs. the UK?

Because the US gallon (3.785 L) and UK imperial gallon (4.546 L) are different sizes. A car traveling a given distance uses the same volume of fuel regardless of where it is. But dividing that distance by a smaller US gallon gives a smaller MPG number than dividing by a larger UK gallon. A car rated 30 MPG (US) is rated approximately 36 MPG (UK).

Is L/100km better or worse than MPG for comparing efficiency?

Neither is inherently better. L/100km measures consumption (how much fuel you use), while MPG measures efficiency (how far you go per unit of fuel). L/100km is arguably more intuitive for comparing fuel costs because you can directly calculate fuel needed for a trip: liters = (km / 100) x L/100km. MPG requires an extra step to get to fuel cost.

What does EPA fuel economy mean?

The US Environmental Protection Agency (EPA) tests fuel economy in standardized city and highway driving cycles. The combined rating is a weighted average (55% city, 45% highway). Real-world efficiency typically varies from the EPA rating based on driving habits, traffic, climate, and vehicle condition.

How do I calculate fuel cost from L/100km?

Multiply (trip distance in km / 100) by L/100km to get liters needed. Then multiply by fuel price per liter. Example: 400 km trip at 8 L/100km = 32 liters x $1.50/L = $48.

Is the fuel efficiency converter free?

Yes. ToolHQ's fuel efficiency converter is completely free, with no account, no sign-up, and no usage limits.

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The short version

The most critical thing to understand about fuel efficiency conversion is that US MPG and UK MPG are not the same unit; the UK gallon is 20% larger, so UK MPG numbers run about 20% higher for the same vehicle. The second most important thing: L/100km runs in the opposite direction from MPG (lower is better). Use the conversion formula L/100km = 235.215 / MPG (US) or 282.481 / MPG (UK) for precise conversions, or use ToolHQ's converter to get all four units simultaneously. 30 MPG (US) = 36 MPG (UK) = 7.84 L/100km = 12.75 km/L.

For related tools, ToolHQ's fuel cost calculator turns your efficiency rating into a trip or monthly cost, and ToolHQ's length converter handles miles to kilometer conversions. Explore more converter tools at ToolHQ.

Convert fuel efficiency free at ToolHQ

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