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 = 235.214583 ÷ MPG (US), while the UK's imperial gallon changes the constant to 282.481 ÷ 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
Every conversion factor used on this page is checked against internationally recognized reference standards — US EPA fuel-economy conversion conventions and NIST Handbook 44 volume standards — rather than approximated or rounded for display. Where a constant is fixed by international definition (such as 1 inch = 2.54 cm, or standard gravity = 9.80665 m/s²), we use the exact defined value. Where a figure is a practical industry convention rather than a physical constant, that distinction is stated explicitly above so results are never presented with false precision.
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 | 6.37 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 | 14.87 km/L | Efficient compact car |
| 45 MPG | 5.23 L/100km | 19.11 km/L | Hybrid vehicle |
| 55 MPG | 4.28 L/100km | 23.38 km/L | High-efficiency hybrid |