Fuel Economy Converter

What it does

Convert fuel economy between regional formats: MPG (US), MPG (UK Imperial), L/100km (Europe, Australia), and km/L (Japan, parts of Asia). Tool produces all four values at once with a tier label so you know whether 35 MPG is “efficient” (yes for sedans), “average” (yes for SUVs), or “poor” (yes for pickup trucks).

The math is non-trivial: US gallons (3.785 L) and UK gallons (4.546 L) differ by 20%, so 30 MPG (US) ≈ 36 MPG (UK), same actual efficiency. L/100km is consumption-per-distance (lower is better) while MPG and km/L are distance-per-consumption (higher is better) — they scale inversely. Conversions: MPG (US) × 0.4251 = km/L; 235.21 / MPG (US) = L/100km; UK MPG × 0.354 = km/L. Many car reviews mix these without specifying — a critical distinction when comparing global cars.

Why L/100km is more intuitive for budgeting: it scales linearly. Going from 8 L/100km to 4 L/100km cuts fuel cost in half. Going from 30 MPG to 60 MPG looks like “double the efficiency” but actually saves only 50% of fuel for the same distance — same as L/100km math. EU regulators chose L/100km to make fuel-cost differences obvious to consumers; the EPA in the US has added it as a secondary metric on EPA labels for the same reason.

How to use it

1. Enter the fuel-economy value you have (e.g., 30 from a US car review).
2. Pick the source unit: MPG (US), MPG (UK), L/100km, km/L.
3. Read the converted values in all four units simultaneously.
4. Use the tier label to interpret the value — what's “good” varies by car class.
5. When comparing cars from different markets, normalize all to the same unit before comparing.

When to use this tool

• Comparing cars across markets (US vs UK vs Japanese model).
• Reading international car reviews that use L/100km when you're used to MPG.
• Calculating fuel cost for international travel or relocation planning.
• Engineering / fleet-management contexts where standardized metrics matter.

When not to use it

• EVs (use kWh per 100 miles or MPGe — gas-equivalent metrics differ).
• Diesel-specific calculations — same conversion math, but compare to diesel benchmarks (typically 25-35% better than gasoline).
• Mixed propulsion (PHEVs) — fuel economy varies by charge state and trip length; single-number conversions oversimplify.
• Track / racing fuel use — different metrics (gallons per lap, fuel per session) used in motorsport contexts.

Common use cases

• Reading a UK car review showing 50 MPG (UK) and converting to know that's 41 MPG (US).
• Buying a vehicle in Europe for export — modeling US fuel cost from EU's published L/100km figure.
• Comparing competing models when one shows MPG and the other shows L/100km in marketing.
• Setting target fuel-economy for international engineering / regulatory compliance.