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The detailed guide below is currently available in English.
The fill-to-fill method
On-board trip computers estimate economy from injector flow; the honest number comes from the pump. Fill the tank, reset the trip meter, drive normally, and fill again. The miles between the two fills divided by the gallons it took to top up the second time is your real fuel economy — no estimates, no lag. The only rule is to stop at the same point each time (automatic shutoff works fine).
MPG and L/100km measure different things
Miles per gallon grows forever as a car gets thriftier — going from 25 to 50 mpg saves 2 gallons per 100 miles, the same as going from 12.5 to 16.6. Liters per 100 km is the inverse view: it shows consumption directly, so each improvement looks like what it is. If you compare vehicles, converting between the two keeps honest math in the conversation.
よくある質問
Why fill the tank both times?
So the gallons you pump exactly equal the gallons burned. If the fill levels differ, some fuel is unaccounted for and the calculation drifts.
What is a good MPG?
Modern small cars and hybrids commonly reach 35–55 mpg, midsize crossovers land near 25–32, and large trucks often sit at 15–20. Your own fill-to-fill number is the only one that reflects how and where you actually drive.
Why does my mileage drop in winter?
Cold engines run richer, gasoline blends shift seasonally, idling to warm up adds fuel with no miles, and snow or rolling resistance grows. A 10–20% winter drop is normal.