OTHER · FUEL ECONOMY CONVERTER
Fuel Economy Converter Calculator
Convert fuel economy between MPG (US), MPG (UK/Imperial), L/100km, and km/L. Handles the inverted L/100km relationship correctly using exact NIST factors.
About This Calculator
Convert fuel economy between US MPG, UK (Imperial) MPG, litres per 100 km, and kilometres per litre. US and UK gallons differ by about 20% — each is labelled explicitly so you never mix them up.
How It Works
Enter a value and pick the units. Fuel economy is an inverted relationship — L/100km rises as efficiency falls — so the converter normalises everything through kilometres per litre using exact distance and volume factors, never a single ratio.
The Formula
Every value is first converted to km/L using exact primitives (1 mile = 1.609344 km; 1 US gallon = 3.785411784 L; 1 Imperial gallon = 4.54609 L). L/100km is the inverted unit: L/100km = 100 ÷ (km/L), so a value of 0 has no meaningful conversion.
Frequently Asked Questions
- Why is US MPG different from UK MPG?
- The US gallon (3.785 L) is smaller than the Imperial gallon (4.546 L). The same car shows a higher MPG figure in the UK simply because a UK gallon holds about 20% more fuel.
- Why isn't MPG just a fixed multiple of L/100km?
- They are inversely related — more miles per gallon means fewer litres per 100 km. You cannot multiply by a single constant; you must invert through km/L, which this tool does.
- What is a good fuel economy figure?
- As a rough guide, 40 MPG (US) ≈ 5.9 L/100km is efficient for a petrol car, while 25 MPG (US) ≈ 9.4 L/100km is average for a larger vehicle.
Estimates only. Coverage figures (sq ft/gallon, bag yield, BTU/sq ft) are industry rules of thumb with real-world variance. Verify quantities with your supplier before purchasing.