Fuel Economy Converter
Convert between MPG (US) and liters per 100 km.
Input sheet
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The US measures fuel economy as miles per gallon (higher is better), while most of the world uses liters per 100 km (lower is better). Because the two run in opposite directions, you can't just multiply — this tool handles the inversion for you.
How it works
MPG (US) and L/100km are inverses linked by the constant 235.215, so 235.215 ÷ value flips either direction.
MPG and L/100km are inverse measures, linked by a single constant. The conversion is 235.215 divided by your value, and the same formula works in both directions — it's its own inverse.
The reason is unit cancellation: US gallons per mile converts to liters per 100 km through fixed factors that collapse into the constant 235.215, so one division flips either way.
L/100km = 235.215 ÷ MPG (and MPG = 235.215 ÷ L/100km).
Worked examples
Convert 30 MPG (US) to liters per 100 km. → 7.8 L/100km
235.215 ÷ 30 = 7.84 L/100km.
Convert 8 L/100km to MPG (US). → 29.4 MPG (US)
235.215 ÷ 8 = 29.40 MPG (US).
Tips & gotchas
- Higher MPG and lower L/100km both mean better economy — they move in opposite directions, so a 'bigger is better' habit fails here.
- Because the relationship is inverse, equal MPG gains matter less at high economy. Going 10→20 MPG saves far more fuel than 40→50 MPG over the same distance.
- This uses the US gallon (3.785 L). UK MPG figures use the larger imperial gallon and read about 20% higher for the same real economy.
- For trip cost, convert to L/100km, multiply by distance ÷ 100, then by fuel price per liter.
FAQ
Why can't I convert MPG to L/100km by simple multiplication?
Because one is distance-per-fuel and the other is fuel-per-distance — they're inverses. You divide the constant 235.215 by your figure instead of multiplying.
Does this use US or UK gallons?
US gallons (3.785 L), which is why the constant is 235.215. UK 'imperial' MPG uses a larger gallon and a different constant (282.481).
Is a lower L/100km better or worse?
Better. L/100km measures fuel used per fixed distance, so a smaller number means the car burns less fuel — the opposite sense to MPG.
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