Fuel Consumption Converter — MPG, L/100km, km/L

Real-world use cases

• Read a foreign car review without a calculator

  A European review praises a hatchback at 5.5 L/100km and you think in MPG. Drop 5.5 into the L/100km field and the tool shows about 42.8 MPG (US) instantly, plus the UK MPG and km/L next to it. No more squinting at a spec sheet trying to decide whether 5.5 is good — see it in the unit your gut already calibrated to and judge it in one glance.

• Compare a US-spec and a UK-spec version of the same model

  The brochures list 32 MPG in the US and 38 MPG in the UK and you suspect they are the same car. Convert both to L/100km: 32 MPG (US) is about 7.35 and 38 MPG (UK) is about 7.43 — close enough to confirm it is one car measured two ways, with the gap explained entirely by the larger Imperial gallon rather than a real efficiency difference.

• Fill in a fuel-economy field that wants a different unit

  A trip-cost spreadsheet or a fleet form asks for km/L but your car is rated in MPG, or an emissions form wants L/100km. Type your known value, pick its unit, and copy the exact figure in the unit the form demands. The one-click copy on each row drops a clean number straight into the cell with no rounding by hand.

• Sanity-check a fuel-economy claim before you trust it

  A used-car listing brags about 70 MPG. Convert it: 70 MPG (US) is about 3.36 L/100km, which is hybrid-or-diesel territory for a small car and implausible for a big petrol SUV. Seeing the L/100km figure makes an inflated or mislabelled claim obvious, especially when the seller quietly used UK MPG to make the number look bigger.

Common pitfalls

• Treating MPG and L/100km as if you just multiply by a constant. They are inverse units, so you must take a reciprocal. 30 MPG is NOT some fixed multiple toward L/100km — it is 235.215 / 30 = 7.84. Multiply when you should divide and you will get a wildly wrong, often backwards, answer.

• Mixing up US and UK gallons. They differ by about 20 percent (3.785 L vs 4.546 L), so a number that looks great might just be a UK MPG quoted as if it were US. Always confirm which gallon a figure uses before comparing two cars.

• Forgetting which direction means efficient. With L/100km smaller is better, but with MPG and km/L bigger is better. People glance at two numbers in two units and pick the bigger one as the winner, which is exactly wrong half the time. Convert to one unit first, then compare.

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