Gas Mileage Calculator
Calculate your vehicle's fuel efficiency in MPG or L/100km and estimate trip costs.
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Fuel economy
👍 Good efficiency
Fuel cost
How to use the Gas Mileage calculator
- Select your preferred calculation system (US or Metric).
- Enter the distance you traveled since your last fill-up.
- Enter the amount of fuel it took to refill the tank.
- (Optional) Enter the price per gallon/liter to see your cost per mile/km.
- Results are shown in both MPG and L/100km, so you can compare with car specs from any country.
Formula
US MPG = Miles Driven ÷ Gallons Used
Metric L/100km = (Liters Used ÷ Kilometers Driven) × 100
Metric km/L = Kilometers Driven ÷ Liters Used
Converting: L/100km = 235.215 ÷ MPG (US), and MPG = 235.215 ÷ L/100km
History & interesting facts
Did you know?
Cruising at 55 mph instead of 75 mph can improve your gas mileage by up to 20%! High speeds encounter exponential aerodynamic drag, forcing your engine to burn more fuel just to push through the air.
Origin & history
Fuel economy standards were first heavily regulated in the United States by the Corporate Average Fuel Economy (CAFE) standards enacted by Congress in 1975. This was a direct response to the 1973-74 Arab Oil Embargo, which caused massive fuel shortages and quadrupled gas prices. By standardizing and mandating higher miles per gallon (MPG) across automaker fleets, nations sought to reduce energy dependency.
Fascinating facts
- 1
In the US, efficiency is measured in MPG (Miles Per Gallon). Higher is better.
- 2
In most of the metric world, efficiency is measured in L/100km (Liters per 100 kilometers). Lower is better.
- 3
Properly inflating your tires can improve your gas mileage by up to 3%.
Frequently asked questions
How do I calculate my exact gas mileage?
To find your actual gas mileage, fill your tank completely and reset your trip odometer. Drive normally until you need to fill up again. Refill the tank completely. Divide the miles driven on the trip odometer by the number of gallons it took to refill the tank.
Why is city MPG always lower than highway MPG?
City driving involves constant stopping, idling, and accelerating. Accelerating a heavy vehicle from a dead stop requires massive amounts of energy (fuel). Highway driving maintains a steady speed and momentum, which is much more efficient unless you are speeding excessively.
How do I convert MPG to L/100km?
Divide 235.215 by the MPG figure (US gallons). For example, 30 MPG = 235.215 ÷ 30 = 7.84 L/100km. The same formula works in reverse: 6 L/100km = 235.215 ÷ 6 = 39.2 MPG. For UK (imperial) MPG, use 282.481 instead.
Does turning off the AC save gas?
Yes, but it depends on your speed. At low speeds, rolling down the windows is more efficient than running the AC compressor. At highway speeds, however, open windows create so much aerodynamic drag that it actually burns more fuel than simply using the AC!