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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.

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 dekaliter. 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.