MPG Calculator

Measuring real fuel economy

Your car's trip computer is an estimate — this calculator gives you the real figure. Fill up, drive, fill up again, and enter the distance driven and the fuel it took. You'll get miles per gallon plus the metric equivalents and, optionally, your cost per mile.

The numbers explained

• MPG = miles ÷ gallons.
• L/100 km — lower is better; the standard measure in most of the world.
• km/L — higher is better; common in Asia.
• Cost per mile = (gallons × price) ÷ miles.

FAQ

How do I measure accurately?

Use the "full-to-full" method: fill the tank completely, reset your trip meter, drive normally, then refill and note the gallons added. That refill amount is exactly the fuel you used for those miles.

Does it support US or UK (imperial) gallons?

The MPG figure uses whatever gallon your fuel was sold in — a US gallon is 3.785 liters and a UK gallon is 4.546 liters, so the two scales aren't interchangeable. For an unambiguous comparison, check the L/100 km or km/L figures, which are based on liters.

Why is my real-world MPG lower than the EPA rating?

Window-sticker ratings come from controlled lab tests, while your number reflects real driving — short trips, cold starts, city stop-and-go, A/C use, and a heavy right foot all lower it. A figure 10–20% below the official rating is common and usually normal.

How is L/100 km different from MPG?

They're inverses: MPG measures distance per unit of fuel (higher is better), while L/100 km measures fuel per fixed distance (lower is better). The calculator shows both so you can read fuel economy in whichever convention you're used to.

Is this calculator free and private?

Yes — it's free with no sign-up, works on any phone browser, and runs entirely in your browser, so your distance, fuel, and cost figures are never sent anywhere.