Fuel Economy Converter Free Online
Convert between fuel economy units instantly. Supports US mpg, UK mpg, liters per 100 km, and kilometers per liter. Compare a US-spec car (mpg) to an EU-spec car (L/100km) or a Japanese spec (km/L) on equal footing.
All Conversions
Pro — bulk batch conversion, API access, history & favorites
API access · Priority queue · Team workspace
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How It Works
Enter a Value
Type the number you want to convert into the From input. The conversion runs as you type — no Convert button needed. Decimals and very small or very large numbers are supported via scientific notation.
Pick Source & Target Units
Use the two dropdowns to choose source (From) and destination (To) units. The result updates automatically. Use the swap button to flip the conversion direction in one click.
See All Conversions
Below the main result, the All Conversions panel shows your input value converted into every supported unit at once — perfect for comparing metric vs imperial side by side.
Fuel Economy Converter Features
Vehicle-ready
L/100km (lower is better) for EU specs, mpg (higher is better) for US/UK, km/L for Japan/India. Compare any car spec sheet.
US vs UK MPG
US gallon = 3.785 L; UK gallon = 4.546 L. So 30 mpg US ≠ 30 mpg UK. UK mpg is always ~20% higher for the same actual efficiency.
EU L/100km
Europe lists fuel use, not distance per fuel. 7 L/100km means a car uses 7 liters to drive 100 km. Lower number = better economy.
Inverse Math
Unlike linear units, fuel economy is inverse: doubling mpg halves L/100km. We use the exact formula 235.21 / mpg = L/100km for US, 282.48 for UK.
Live Conversion
Result updates as you type. Compare a 32 mpg US sedan to a 7.4 L/100km EU spec instantly.
100% Private
All math runs in your browser. No tracking, safe for any vehicle data.
Free vs Pro
| Feature | Free | Pro |
|---|---|---|
| All 4 fuel economy units | ||
| Live conversion | ||
| All-units result table | ||
| Bulk CSV / Excel conversion | — | |
| REST API access | — | |
| Custom precision settings | — |
Frequently Asked Questions
Because mpg measures distance per fuel (higher = better), but L/100km measures fuel per distance (lower = better). They are inversely related: L/100km = 235.214583 / mpg US, or L/100km = 282.481 / mpg UK. Doubling mpg halves L/100km.
No. The US gallon (3.785 L) is smaller than the UK imperial gallon (4.546 L), so 1 mpg UK = 1.20095 mpg US. A 30 mpg US car is the same efficiency as a 36 mpg UK car.
Roughly: small efficient car ≈ 6 L/100km (40 mpg US, 47 mpg UK); SUV ≈ 10 L/100km (24 mpg US, 28 mpg UK); hybrid ≈ 4 L/100km (59 mpg US, 71 mpg UK); EV uses kWh/100km instead.
Multiply km/L by 2.3521 to get mpg US, or by 2.8248 to get mpg UK. Or use this converter directly.
Because EVs use electricity, not liquid fuel. Common units: kWh/100km (EU), miles per kWh (US), Wh/km (engineering). Use the Energy Converter for kWh, then divide by distance manually.