MPG ↔ L/100km.
Converts fuel efficiency between MPG (US or UK) and L/100km. They're inversely related.
Formula: L/100km = 235.215 / MPG (US) or 282.481 / MPG (UK).
Because MPG and L/100km move in opposite directions (higher MPG is better, lower L/100km is better), comparing efficiency improvements across the two systems isn't intuitive without converting to a common unit first.
30 MPG (US) ≈ 7.84 L/100km.
UK gallon (4.546 L) is larger than US (3.785 L), so UK MPG numbers are always higher for the same real efficiency.
L/100km scales linearly with fuel use — halving it halves fuel cost. MPG is inverted, so improvements are less intuitive.
EVs typically report efficiency in miles/kWh or kWh/100km instead of MPG, since they consume electricity rather than liquid fuel — the two aren't directly comparable without a conversion factor.