⛽ Fuel Economy Converter
Convert MPG (US and UK), km/L, and L/100km — the three dominant fuel efficiency standards worldwide.
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Common Fuel Economy Conversions
| Input | Unit | Result | Unit |
|---|---|---|---|
| 30 | MPG (US) | 7.8404754 | L/100km |
| 7 | L/100km | 33.602038 | MPG (US) |
| 40 | MPG (UK) | 33.306924 | MPG (US) |
| 15 | km/L | 35.282139 | MPG (US) |
| 50 | MPG (US) | 21.257214 | km/L |
| 5 | L/100km | 20 | km/L |
Popular Conversions
Formula Reference
MPG (US) ↔ L/100km: MPG = 235.215 ÷ L/100km (reciprocal — not linear) MPG (UK) ↔ MPG (US): US MPG = UK MPG × 0.8327 (imperial gallon is 20% larger) km/L ↔ MPG (US): MPG = km/L × 2.3521
About Fuel Economy Conversions
Fuel economy measures how efficiently a vehicle uses fuel. In the United States, efficiency is expressed as miles per gallon (MPG) — the higher the number, the more efficient the vehicle. Most other countries use liters per 100 kilometers (L/100km), where a lower number means better efficiency. This inverse relationship means you cannot simply multiply or divide to convert between them — a different formula is required.
The United Kingdom uses its own MPG figure based on the imperial gallon, which at 4.546 liters is about 20% larger than the US gallon (3.785 liters). A car rated at 40 MPG in the UK delivers only about 33 MPG by the US standard. This distinction matters when comparing vehicles across markets or reading foreign reviews. Always check which gallon standard is being used.
The conversion between L/100km and MPG (US) is: MPG = 235.215 ÷ L/100km. This reciprocal relationship means improvements in L/100km are not linear in their MPG impact — going from 10 L/100km to 9 L/100km is a much smaller MPG gain than going from 6 L/100km to 5 L/100km. This is why many fuel economy analysts prefer L/100km for accurately representing real-world savings.
Frequently Asked Questions
How do I convert MPG to L/100km?
Divide 235.215 by the MPG figure to get L/100km. For example, 30 MPG = 235.215 ÷ 30 = 7.84 L/100km. The same formula works in reverse: L/100km to MPG = 235.215 ÷ L/100km. This reciprocal relationship means the two scales are not proportional.
What is the difference between US MPG and UK MPG?
The US gallon is 3.785 liters while the UK imperial gallon is 4.546 liters — about 20% larger. A vehicle achieving 40 UK MPG therefore delivers only about 33.3 US MPG. Always verify which standard is used when comparing international fuel economy figures.
Is higher MPG always better?
Yes — a higher MPG number means the vehicle travels farther on each gallon of fuel, so it is more fuel-efficient. The reverse is true for L/100km: a lower L/100km value means less fuel consumed per distance traveled, so lower is better. This opposite intuition trips up many people switching between systems.
What is considered good fuel economy?
A fuel-efficient modern passenger car typically achieves 35–50 MPG (US) on a combined cycle, or about 4.7–6.7 L/100km. Hybrid vehicles commonly exceed 50 MPG. SUVs and trucks generally fall in the 15–30 MPG range. Electric vehicles use a 'MPGe' (MPG equivalent) rating — typically 80–130 MPGe.
Why does fuel economy worsen at highway speeds?
Aerodynamic drag increases with the square of speed — doubling your speed quadruples drag force. At highway speeds above roughly 55 mph (88 km/h), overcoming wind resistance consumes a growing share of engine output. Most vehicles achieve peak fuel economy at 45–55 mph. City driving suffers from frequent braking and idling, while true highway cruising above 70 mph also sees reduced MPG.
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All conversion results are provided for general informational purposes only. Our formulas use internationally recognized conversion factors; however, rounding may affect precision. Do not rely on these results for professional, medical, legal, or engineering decisions without independent verification. Read our full disclaimer.