Fuel Economy Converter
Convert fuel economy between MPG, L/100km and km/L.
Results update as you type.
About this calculator
A fuel economy converter translates a vehicle efficiency figure between US miles per gallon, UK miles per gallon, liters per 100 km, and kilometers per liter. Because L/100km measures fuel used per distance while the others measure distance per fuel, the tool converts through L/100km rather than a single multiplier.
That inverse relationship is the catch: a higher MPG or km/L means better economy, but a higher L/100km means worse economy. The bridging constants are L/100km = 235.215 ÷ MPG(US) and L/100km = 282.481 ÷ MPG(UK), reflecting that a UK gallon is about 20% larger than a US gallon.
Worked example: to convert 30 US MPG to L/100km, divide 235.215 by 30, giving about 7.84 L/100km. The same car rated in UK MPG would read about 36 mpg. A results table shows the figure in all four measures at once so you can compare cars quoted in different systems.
Frequently asked questions
How do I convert MPG to L/100km?
They are inversely related: L/100km = 235.215 ÷ MPG (US). So 30 US mpg is about 7.84 L/100km. A higher mpg but a lower L/100km both mean better economy.
Why are US and UK MPG different?
A UK gallon is about 20% larger than a US gallon, so the same car scores higher mpg in UK figures. Always note which gallon a quoted mpg uses.
What is km/L?
Kilometers per liter is used in parts of Asia and is proportional to mpg. Convert via L/100km = 100 ÷ (km/L).
Is a higher or lower number better for fuel economy?
It depends on the unit. Higher is better for MPG and km/L (more distance per fuel), while lower is better for L/100km (less fuel per distance). This fuel economy converter shows all four so the direction is never ambiguous.
How do I convert L/100km to MPG?
Divide 235.215 by the L/100km value to get US MPG, or 282.481 to get UK MPG. So 8 L/100km is about 29.4 US mpg or 35.3 UK mpg.
Why can’t I just multiply MPG by a fixed number to get L/100km?
Because the two are inversely related, not proportional: doubling MPG halves L/100km. That is why the conversion divides a constant by your figure instead of multiplying it.
API — use this calculator from code
Call this calculator as a free JSON endpoint — no key required. Send the field values below as query parameters or JSON. Read the full API docs →
Endpoint
GET https://calculator.free/api/v1/fuel-economy/curl
curl "https://calculator.free/api/v1/fuel-economy/?amount=1&from=mpgus&to=l100km"JavaScript fetch()
const r = await fetch(
"https://calculator.free/api/v1/fuel-economy/?" + new URLSearchParams({
"amount": "1",
"from": "mpgus",
"to": "l100km"
}));
const data = await r.json();
console.log(data.results);Results are estimates for general guidance only, not financial, medical or tax advice.