Fuel Efficiency Calculator

Convert Fuel Efficiency Units

Enter a value in any one field — all others will be calculated automatically.

Calculate Efficiency from Trip Data

--

Understanding Fuel Efficiency Measurements

Fuel efficiency — or fuel economy — describes how far a vehicle travels per unit of fuel consumed. Different countries use different units: the USA uses miles per gallon (MPG), Europe and most of Asia use litres per 100 kilometres (L/100km), and some countries use kilometres per litre (km/L). Understanding these units and converting between them helps you compare vehicles and fuel costs across different markets.

L/100km vs MPG — Which Is Better When Lower?

This is a common source of confusion. With L/100km, a lower number means better efficiency (less fuel per distance). With MPG, a higher number means better efficiency (more distance per gallon). This means you cannot simply compare percentage improvements in the two scales linearly — a jump from 10 to 5 L/100km doubles fuel efficiency, but the equivalent MPG change is much less dramatic at high MPG values.

US Gallon vs UK Imperial Gallon

The US gallon and the UK (Imperial) gallon are different volumes: 1 US gallon = 3.785 litres, while 1 UK gallon = 4.546 litres. A car rated at 30 MPG (US) is equivalent to 36 MPG (UK) and 7.84 L/100km. Always check which gallon a car's MPG rating is based on when comparing international figures.

Tips to Improve Fuel Efficiency

  • Maintain correct tyre pressure — under-inflated tyres increase rolling resistance and fuel consumption by up to 3%.
  • Drive smoothly — avoid harsh acceleration and braking. Anticipating traffic flow is the single biggest factor in real-world fuel economy.
  • Reduce speed on motorways — fuel consumption increases significantly above 90–100 km/h due to aerodynamic drag.
  • Remove roof racks and carriers when not in use — they increase drag substantially.
  • Keep air conditioning use to a minimum at low speeds; it can reduce efficiency by 5–15%.

Frequently Asked Questions

How do I convert MPG to L/100km?
For US MPG: L/100km = 235.214 ÷ MPG. For UK MPG: L/100km = 282.481 ÷ MPG. You can also use the converter above by entering your MPG value.
What is a good fuel consumption for a car?
For a modern petrol passenger car, under 7 L/100km (over 33 MPG US) is considered efficient. Under 5 L/100km (over 47 MPG US) is excellent, typical of hybrids. Diesel cars typically achieve 15–20% better L/100km than equivalent petrol models.
Does official MPG match real-world fuel economy?
Official lab test figures typically overestimate real-world fuel economy by 15–30%. Real-world consumption depends on driving style, road conditions, climate, payload, and vehicle maintenance.
What is the difference between fuel efficiency and fuel economy?
The terms are often used interchangeably. Technically, fuel economy measures how far you travel per unit of fuel (MPG, km/L), while fuel efficiency refers to how effectively the engine converts fuel energy into motion. Higher fuel economy generally means higher efficiency.