Free Fuel Economy Converter
Convert fuel economy units instantly — MPG (US/UK), L/100km, km/L, mL/km. Type into any field and all others update. Free, symmetrical, no sign-up.
Exact Conversion Formula & Multipliers
Fuel economy conversion is a reciprocal relationship, not a simple multiplication: L/100 km = 235.2145833 ÷ MPG (US), while the UK's imperial gallon changes the constant to 282.4809363 ÷ MPG (UK), since a US mpg and a UK mpg measure different-sized gallons over the same mile. Because the relationship is inverse, a 'higher is better' unit (mpg) converts to a 'lower is better' unit (L/100 km), which is a common source of confusion this converter's clear labeling is meant to avoid.
Practical Real-World Scenarios
- Buying an imported vehicle: comparing a US-market car's mpg rating to a European model's L/100 km figure requires converting — and remembering that the two scales run in opposite directions.
- Road trip budgeting: estimating fuel costs across a US-Canada or UK-Europe trip means reconciling mpg and L/100 km figures, plus gallon-size differences if crossing into imperial-gallon territory.
- Fleet and logistics management: multinational vehicle fleets track efficiency in whichever unit each country's regulations require, and comparing performance across the fleet requires standardizing to one unit.
Historical & Technical Background
Miles per gallon became the standard US fuel economy metric alongside the country's broader adoption of imperial units for road travel, while L/100 km emerged as the natural metric-system equivalent — chosen as consumption per fixed distance rather than distance per fixed volume, which is arguably more intuitive for budgeting fuel costs on a known trip length. The reversal in direction (higher mpg is good, lower L/100 km is good) is simply a byproduct of which quantity — distance or volume — each system chose to hold fixed.
Precision & Accuracy Statement
Conversion factors use the exact defined values given in NIST Special Publication 811 and the BIPM SI Brochure wherever such a definition exists (for example 1 lb = 0.45359237 kg, 1 in = 2.54 cm, 1 US gal = 3.785411784 L, g₀ = 9.80665 m/s²); derived factors are computed from those definitions rather than copied as rounded figures. Results are calculated in double-precision floating point and shown to 10 significant digits, so the last digit can differ by one unit of rounding. The rounded figures in the text and tables above are for reading convenience.
How This Converter Works
Fuel economy uses inverse units — MPG measures distance per volume (higher = better), while L/100km measures volume per distance (lower = better). Our converter handles both systems including UK and US gallon differences.
Common Conversions
| MPG (US) | L/100km | km/L | Vehicle Type |
|---|---|---|---|
| 15 MPG | 15.68 L/100km | 6.38 km/L | Large truck or SUV |
| 25 MPG | 9.41 L/100km | 10.63 km/L | Average passenger car |
| 35 MPG | 6.72 L/100km | 14.88 km/L | Efficient compact car |
| 45 MPG | 5.23 L/100km | 19.13 km/L | Hybrid vehicle |
| 55 MPG | 4.28 L/100km | 23.38 km/L | High-efficiency hybrid |