400 miles on 12 gallons
Here’s the gas mileage for 400 miles driven using 12 gallons of fuel.
Different numbers? Use the gas mileage calculator above.
About the gas mileage calculator
Gas mileage, or fuel economy, is simply the distance you can travel per unit of fuel. In the US it's expressed as miles per gallon (mpg), calculated with one formula: mpg = miles driven ÷ gallons used. Fill up, reset your trip odometer (or note your mileage at the last fill-up), drive until your next fill-up, then divide the miles covered by the gallons it took to refill the tank.
Because fuel economy is expressed differently around the world, this calculator also converts your mpg into the two metric equivalents you'll see on imported vehicles or in other countries. Liters per 100km works in the opposite direction from mpg — a lower number means better efficiency, since it's asking "how much fuel does it take to go 100km" rather than "how far does one unit of fuel go." The conversion is L/100km = 235.214 ÷ mpg.
Kilometers per liter, on the other hand, moves in the same direction as mpg: a higher number means better efficiency, since it answers the same underlying question ("how far per unit of fuel") just in metric units. The conversion is km/L = mpg × 0.425144.
Real-world mpg varies more than most drivers expect — highway driving, city stop-and-go traffic, cargo weight, tire pressure, and even outside temperature can shift your actual mileage well away from a vehicle's window-sticker EPA estimate. Calculating your own mpg from actual fill-ups, ideally averaged over several tanks, gives a far more accurate picture of what you're really getting than the manufacturer's rating alone.
This calculator uses total miles and total gallons for a single fill-up period rather than requiring separate odometer readings, so you can plug in numbers directly from a trip log, a road trip, or your fuel receipts without doing subtraction first.
Gas mileage calculator questions
How to calculate mpg and convert it to metric fuel economy.
How do I calculate gas mileage (mpg)?
Divide the miles driven by the gallons of fuel used: mpg = miles driven ÷ gallons used. For example, driving 300 miles on 10 gallons is 300 ÷ 10 = 30 mpg.
How do I convert mpg to liters per 100km?
Divide 235.214 by your mpg: L/100km = 235.214 ÷ mpg. A lower L/100km number means better fuel economy, since it measures fuel needed per fixed distance rather than distance per unit of fuel.
How do I convert mpg to kilometers per liter?
Multiply your mpg by 0.425144: km/L = mpg × 0.425144. Unlike L/100km, a higher km/L number means better fuel economy, matching the same direction as mpg.
Why is my real-world gas mileage different from the EPA estimate?
EPA window-sticker ratings are measured under standardized test conditions. Real-world mpg varies with driving style, highway vs. city driving, cargo weight, tire pressure, and temperature, so your actual mileage often differs from the rating.
How many miles per gallon is considered good gas mileage?
It depends on the vehicle type: compact and hybrid cars often get 35-50+ mpg, midsize sedans typically get 25-35 mpg, and trucks or SUVs often get 15-25 mpg. Compare your result to your specific vehicle's EPA rating for context.
Do I need my odometer readings to use this calculator?
No — just enter the total miles driven and total gallons used for that driving period or fill-up. If you only have odometer readings, subtract the starting reading from the ending reading first to get miles driven.