MPG vs L/100km: How to Compare Fuel Economy Across Markets
A practical guide to converting between US/UK MPG and L/100km, plus tips for comparing cars worldwide.
MPG vs L/100km: why does fuel economy use two systems?
Fuel economy measures how far a vehicle travels per unit of fuel. The problem is that two competing systems are in widespread use: the United States and the United Kingdom report miles per gallon (MPG), while most of Europe, Asia, and Latin America report liters per 100 kilometers (L/100km). They are mathematically inverse — a "higher" MPG means better efficiency, while a "lower" L/100km means better efficiency.
Converting between them is more involved than a simple factor because the gallon itself differs: the US gallon is 3.785 L, while the imperial (UK) gallon is 4.546 L. That is why a UK MPG and a US MPG are not directly comparable.
Common use cases
- Comparing cars across markets: Buying guides often quote fuel economy in the "wrong" unit for the reader
- Importing vehicles: Converters help when reading spec sheets from another country
- Trip planning: Estimate fuel needed for a road trip with a foreign rental car
- Fleet management: International fleets need consistent efficiency reporting
- Sustainability reporting: Companies report emissions in L/100km, while employees discuss MPG
Method 1: Use UtilBoxx's free fuel economy converter (Recommended)
Our fuel economy converter handles both US and imperial gallons, plus L/100km, km/L, and miles per gallon (US and UK). Here is how to use it:
- Go to utilboxx.com/en/tools/unit/fuel
- Enter a value in any field (L/100km, MPG US, MPG UK, km/L)
- All other fields update instantly
- Toggle between US and UK gallons with a single switch
- Copy any value with one click
Why this method works:
- Handles both US and imperial gallons correctly
- Real-time conversion as you type
- Mobile-friendly with large fields
- No ads, no signup, no tracking
- 100% in-browser, your data never leaves the device
Method 2: Use the manual formulas
If you need to do the math by hand:
- L/100km to MPG (US) = 235.215 / (L/100km)
- L/100km to MPG (UK) = 282.481 / (L/100km)
- MPG (US) to L/100km = 235.215 / MPG
- MPG (UK) to L/100km = 282.481 / MPG
- km/L to MPG (US) = km/L × 2.352
For example, 7 L/100km = 235.215 / 7 ≈ 33.6 MPG (US).
Method 3: Use a spreadsheet
In Google Sheets or Excel, you can build a small conversion table:
``` = 235.215 / A1 // L/100km to MPG (US) = 282.481 / A1 // L/100km to MPG (UK) = A1 / 2.352 // km/L to MPG (US) = A1 * 0.425144 // MPG (US) to km/L ```
This is great for batch conversion of vehicle data.
Frequently asked questions
Is higher MPG better or lower?
In MPG, higher is better — you travel more miles per gallon. In L/100km, lower is better — you use less fuel per 100 km. The two systems are inversely related.
What is the difference between US MPG and UK MPG?
A US gallon is 3.785 L; a UK (imperial) gallon is 4.546 L. A car rated 30 MPG (US) = 30 / 1.201 ≈ 25 MPG (UK). The numbers are not interchangeable.
What is a "good" fuel economy?
A modern compact car typically achieves 6-8 L/100km (about 30-40 MPG US). Hybrids and EVs do much better. Anything above 10 L/100km (under 24 MPG US) is considered thirsty.
How do I compare cars from different countries?
Use the UtilBoxx fuel economy converter to put both cars in the same unit, or use the standard L/100km metric which is increasingly common worldwide.
Conclusion
Whether you are browsing a US auction site, comparing European hatchbacks, or planning a road trip abroad, the UtilBoxx fuel economy converter makes the math disappear.