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Gas Mileage Calculator

Get your MPG and L/100km from distance and fuel used.

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How to use

  1. 1.Choose your unit system: imperial (miles and US gallons) or metric (kilometers and liters).
  2. 2.Enter the distance you drove and the amount of fuel you used to cover it.
  3. 3.Read your fuel economy instantly below — MPG, L/100km and km/L are all shown at once.

About Gas Mileage Calculator

This gas mileage calculator turns two numbers you already know into your real fuel economy the moment you type them: the distance you drove and the fuel you put in. Pick imperial (miles and US gallons) or metric (kilometers and liters), enter the trip, and it returns your miles per gallon, your liters per 100 km, and your kilometers per liter at the same time, so you get the figure your country uses and the one the rest of the world uses side by side. There is no button to press and nothing is uploaded, so it is fast and private.

What the numbers mean: MPG, or miles per gallon, is a measure of efficiency, so higher is better, and it is simply the miles you drove divided by the gallons you burned. L/100km, or liters per 100 kilometers, is a measure of consumption, so lower is better, and it is the liters used divided by the kilometers driven, multiplied by 100. The two describe the same thing from opposite directions, which is why 30 MPG feels good while 3 L/100km feels good but 30 L/100km does not. They are linked by a fixed conversion: L/100km = 235.214583 divided by MPG (US), so 30 MPG works out to about 7.84 L/100km. km/L is a third view, popular in parts of Asia, and is just kilometers driven divided by liters used.

US gallon versus UK gallon matters more than most people expect. This tool uses the US gallon, which is 3.785411784 liters, the same gallon quoted on American window stickers and by the EPA. The UK, or Imperial, gallon is larger at 4.54609 liters, about 20% bigger, so the very same car scores a higher number in UK MPG than in US MPG even though nothing about it changed. A car rated 30 US MPG is roughly 36 UK MPG. If you compare a US figure with a UK figure directly you will think one car is far thirstier than it is, so always confirm which gallon a quoted MPG uses before comparing.

How to measure your own fuel economy accurately: fill the tank completely and either reset the trip meter or write down the odometer. Drive normally until you need fuel again, then fill completely a second time. The pump tells you exactly how much fuel you used to cover that distance, and those two numbers are what you enter here. Doing this over a full tank, and ideally averaging several tanks, smooths out the noise from a single short trip and gives a number you can trust.

How to use less fuel: keep tires at the correct pressure, since under-inflated tires add rolling resistance; ease off hard acceleration and braking, which waste the most; remove roof boxes and heavy items you are not using; and hold steady speeds, because economy falls sharply at high motorway speeds. To convert the energy or unit figures further, reach for an energy converter, a density converter, or, for electric vehicles, an EV charging cost calculator.

Frequently asked questions

How do I calculate gas mileage (MPG)?
Divide the distance you drove by the fuel you used. In US units, MPG = miles driven / US gallons used, so 300 miles on 10 gallons is 30 MPG. In metric, consumption is liters used / km driven x 100; 40 liters over 500 km is 8 L/100km. Higher MPG and lower L/100km both mean better economy.
What is the difference between MPG and L/100km?
MPG measures efficiency (distance per fuel), so higher is better, while L/100km measures consumption (fuel per distance), so lower is better. They describe the same economy from opposite directions and convert with L/100km = 235.214583 / MPG (US). For example, 30 MPG equals about 7.84 L/100km.
Does this use the US gallon or the UK (Imperial) gallon?
This calculator uses the US gallon, which is 3.785 liters, matching EPA and US window-sticker figures. The UK or Imperial gallon is larger at 4.546 liters, about 20% bigger, so the same car scores a higher number in UK MPG. A car rated 30 US MPG is roughly 36 UK MPG, so always check which gallon a quoted MPG refers to before comparing.
How do I measure my car's real fuel economy?
Fill the tank fully and reset the trip meter or note the odometer. Drive normally until you refuel, then fill fully again. The pump shows exactly how much fuel you used for that distance; enter both numbers here. Averaging several full tanks gives a more reliable figure than a single short trip.
How can I improve my gas mileage?
Keep tires properly inflated to cut rolling resistance, avoid hard acceleration and braking, remove roof boxes and unnecessary weight, and hold steady, moderate speeds since economy drops sharply at high motorway speeds. Regular servicing and using the recommended oil and fuel grade also help.

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