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Metric system: units of volume

Learn about metric units of volume or capacity such as milliliter and liter. Created by Sal Khan.

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Video transcript

Let's think a little bit about the metric system units for volume, or essentially how much space something is taking up in three dimensions. So the base unit in the metric system for volume is the liter. And there's a couple of ways that you can visualize a liter. One way you could think about a liter is if you took a cube that is 10 centimeters deep, 10 centimeters wide, and 10 centimeters tall, then this amount of space that you're taking up, this volume is 1 liter. So this right over here is 1 liter. Another way to connect it to our everyday lives is you've probably gone and bought, or your parents have bought, a 2-liter bottle of something. Oftentimes, it's soda. So those 2-liter bottles are-- as I just mentioned, these are 2 liters. So let me make my best attempt to draw what those bottles look like. They look something like this. At least in the US, oftentimes soda, and other things, will be sold in these 2-liter bottles. So if you take half of this, you are looking at a liter. So liter would be about half of this. So if it's half full, a liter would be about that much. And hopefully, that is consistent or that makes sense relative to this 10 centimeter by 10 centimeter by 10 centimeter cube. Now, if you want to measure things that are a lot smaller than a liter, the typical unit used-- and obviously in the metric system, you can always use the prefixes deci, centi. But the one that's most typically used is the milliliter-- milli-- the milliliter. And we've already seen the prefix milli. It means 1/1,000. So this means 1/1,000 of a liter. Or another way of thinking about it is 1 liter is equal to 1,000 milliliters. And if you wanted to visualize what a milliliter looks like, imagine taking a cube. And instead of making it 10 centimeters on each dimension, make it only 1 centimeter in each dimension. So 1 centimeter wide, 1 centimeter deep, and 1 centimeter high, and then you're looking at a milliliter. And if you want to think about the type of things that are measured in milliliters, you might think things about dosage of medicine. So for example, a typical teaspoon that you might see in your cabinet is going to be a little bit over 4 milliliters, almost 5 milliliters. So that might be good for medicine dosage or maybe small ingredients in some type of a recipe. If you want to go larger than a liter-- and once again, you could use all the metric prefixes. You could use deciliter. You could use hectoliter. But the one that's most typically used is kiloliter. And as the prefix kilo implies, this is equivalent to 1,000 liters. And if you want to visualize this, this actually isn't as large as you might assume it to be. If you just take a cube, and this side, instead of taking each dimension being 10 centimeters, if you were to take a cube where each dimension is exactly 1 meter, so 1 meter deep, 1 meter wide, and 1 meter tall, this volume is equivalent to 1 kiloliter. So you could imagine something like a kilometer would be very useful for measuring, say, the volume of water inside of a swimming pool.