Fuel Economy (MPG) Calculator
Calculate your vehicle’s real-world fuel economy from miles driven and gallons used. Fast, free, and fully client-side.
Calculator Inputs
How the Fuel Economy (MPG) Calculator Works
Calculates your vehicle’s actual fuel economy in miles per gallon (MPG) from a fill-up’s trip distance and gallons used, and converts the result to liters per 100 kilometers (L/100km) for comparison against metric-rated vehicles.
Formula
MPG = Miles Driven / Gallons Used, then L/100km = 235.215 / MPG
235.215 is the standard conversion constant between miles-per-US-gallon and liters-per-100-kilometers, derived from the fixed relationship between miles, gallons, kilometers, and liters.
Calculation Example
Driving 300 miles on 12 gallons: 300 / 12 = 25.0 MPG, or 235.215 / 25 ≈ 9.4 L/100km.
Frequently Asked Questions
Why does my real-world MPG differ from the sticker rating?
EPA sticker ratings come from standardized lab test cycles. Real-world MPG varies with driving style, terrain, weather, tire pressure, and load, and is usually lower than the sticker figure for city driving.
How do I get an accurate reading?
Fill the tank completely, reset your trip odometer, drive normally until the next fill-up, then divide the miles driven by the gallons needed to fill the tank again.
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