MPG Calculator
The MPG Calculator computes your vehicle's actual fuel economy based on distance driven and fuel used, so you can compare it to the manufacturer estimate. Works in U.S. units (miles/gallons → MPG) or metric (kilometers/liters → L/100km). Filling the tank to the same point — usually the first automatic click-off of the pump nozzle — at both the start and end of the measurement period removes the most common source of error in a fill-to-fill MPG calculation. Very short trips also tend to show worse-than-typical fuel economy, since a cold engine and catalytic converter burn more fuel before reaching normal operating temperature.
Switch between U.S. Customary and Metric units.
How This Tool Works
Pick your units, fill your tank completely, reset your trip odometer, drive normally, then refill and enter the distance driven and fuel used since the last fill-up.
Formula & Method
U.S.: MPG = miles driven ÷ gallons used. Metric: L/100km = (liters used ÷ kilometers driven) × 100, and km/L = kilometers ÷ liters.
Example Calculation
U.S. example: You fill up, reset your trip odometer, drive 412 miles, then refill using 13.75 gallons. MPG = 412 ÷ 13.75 ≈ 29.96 MPG (rounds to 30.0 MPG), or about 3.34 gallons per 100 miles. Metric example: 685 km driven on 52 liters gives L/100km = (52 ÷ 685) × 100 ≈ 7.59 L/100km, equivalent to about 13.17 km per liter.
Frequently Asked Questions
Why is my calculated MPG different from the EPA estimate?+
EPA estimates are based on standardized test conditions. Real-world fuel economy varies with driving style, terrain, weather, tire pressure, and vehicle load.
Can I calculate fuel economy in L/100km?+
Yes — switch the unit toggle to Metric and enter your distance in kilometers and fuel used in liters. The result is shown in L/100km and kilometers per liter.
How can I improve my fuel economy?+
Maintaining proper tire pressure, avoiding aggressive acceleration, reducing excess weight, and keeping up with maintenance can all meaningfully improve fuel economy.
Should I calculate over multiple tanks?+
Yes, averaging over several fill-ups gives a more reliable number than a single tank, which can be skewed by a mix of highway and city driving.
Why should I use the trip odometer instead of subtracting total odometer readings?+
The trip odometer is built for exactly this — resetting it to zero at a fill-up eliminates the risk of a subtraction error from writing down two large total-odometer numbers and doing the math later. It also makes it easy to isolate a single fill-to-fill period cleanly.
Can I use this to sanity-check a used car's advertised fuel economy?+
Yes — during a test drive or trial period, do a fill-to-fill measurement and compare the result to the EPA or manufacturer rating. A real-world figure that comes in more than 15–20% below the rated MPG on normal mixed driving can be a sign of engine, transmission, tire pressure, or alignment issues worth investigating before you buy.
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<a href="https://everyfix.net/tools/mpg-calculator/">MPG Calculator</a> by <a href="https://everyfix.net">EveryFix</a>Related Tools
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