Free online calculator
Fuel efficiency calculator
Calculate MPG, km/L, and L/100km.
Fuel efficiency
Enter distance and fuel used to see L/100km, km/L, US MPG, and UK MPG.
How to use this calculator
- 1
Enter the distance
Type how far you drove and select kilometres or miles.
- 2
Enter the fuel used
Type how much fuel you consumed and select litres or US gallons.
- 3
Read all four metrics
The calculator shows L/100km, km/L, US MPG, and UK MPG simultaneously.
- 4
Switch units
Toggle the distance or fuel unit and all results update instantly.
Formula
L/100km: (litres ÷ km) × 100
km/L: km ÷ litres
US MPG: miles ÷ (litres ÷ 3.785 411 784)
UK MPG: miles ÷ (litres ÷ 4.54609)
All inputs are normalised to kilometres and litres first, then converted to miles and gallons for the MPG figures.
Worked example
100 km on 8 L:
L/100km = (8 ÷ 100) × 100 = 8.00. km/L = 100 ÷ 8 = 12.50. Miles = 100 ÷ 1.609 = 62.14. US gal = 8 ÷ 3.785 = 2.113. US MPG = 62.14 ÷ 2.113 = 29.41. UK MPG = 62.14 ÷ (8 ÷ 4.546) = 35.34.
FAQ
What's the difference between US and UK MPG? +
A US gallon is 3.785 L while a UK (imperial) gallon is 4.546 L. The same car travelling 100 miles on 10 litres would show about 37.9 US MPG but 44.4 UK MPG — always check which standard a spec sheet uses.
How do I convert L/100km to MPG? +
To convert L/100km to US MPG, divide 235.21 by the L/100km figure. For UK MPG divide 282.48 by the L/100km figure. This calculator does both conversions automatically.
Is lower L/100km better? +
Yes. L/100km measures how much fuel is used per distance, so a smaller number means better efficiency. The opposite applies to MPG and km/L — higher is better for those metrics.
What fuel unit should I use? +
Use litres if your fuel receipts are in litres (most of the world) and US gallons if you are in the United States. The UK also uses litres at the pump, even though official MPG figures use imperial gallons.
Can I use this for motorcycles or trucks? +
Yes — the calculator works for any vehicle. Just enter the distance and fuel used from any single tank fill-up or multi-tank trip for the most accurate result.
About this calculator
This fuel efficiency calculator converts your distance and fuel used into all four common efficiency figures at once: L/100km, km/L, US MPG, and UK MPG. Use it to compare car specs, track fuel economy over trips, or convert between measurement systems.
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