Getting a sense of meters and centimeters

In this video I'm going to talk about a unit of length known as the meter, which you might have heard of before. It's really probably the most used unit of length in the world.

So the natural question is: how long is a meter? Well, one way to get a rough sense of a meter is to imagine a reasonably tall basketball player, so a good bit taller than your average man.

So a good bit taller than me – I'm about average height – so that's your basketball player there. He's got his basketball, and he might be roughly two meters tall. So this would be two meters, one meter. This lowercase m is short for meter, and then two meters.

Another way to think about a meter is if you took a long step. If you're, let's say, seven or eight years old and if you were to take a long step, you might travel about a meter. So that's your long step right over there. It might be close to a meter. Roughly; it's not necessarily going to be exactly a meter, but it might be close.

Now, a related unit of length is known as the centimeter. You might already recognize that it has the word "meter" in it, and it also has the word "centi." Now, you might already know the word "cent." A hundred cents make a dollar. You might know the word "century" – that's a hundred years.

So, you might say, "Is this a hundred meters?" You'd be kinda close but kinda far off. It's not a hundred meters; it's not bigger than a meter. It's actually a lot smaller than a meter. A centimeter – a hundred of them will equal one meter.

So one way to think about it is if I write it in shorthand: 100, and you normally write it as lowercase c and m. So, 100 centimeters are equal to 1 meter.

So on these pictures right over here, a centimeter would be much smaller than a meter. Right over there, even what I just drew there would be a lot less than a centimeter. And one way to think about a centimeter – it might be if you stick your finger out. Your finger, depending on how large your finger is, might be about a centimeter wide.

As a grown average-sized man, my finger is actually about two centimeters wide. If I take my index finger and if I were to measure it, I would approximate it as about two centimeters. So, a hundred centimeters make up a meter, which hopefully makes a little bit of sense to you.

Now, given what we've just learned about meters and centimeters, let's think about what is better to measure with, depending on the size of the thing. So, if I was looking at a let's say a fairly tall tree of some kind, what would I want to measure that with? Would I be more likely to measure that in meters, or would I be more likely to measure that in centimeters?

Pause this video and think about that. Well, a fairly tall tree is going to be a lot taller than even this basketball player. So normally, people are likely to measure this in meters. A reasonably tall tree could be 10 meters or 20 meters or even, in certain cases, 30 meters or taller.

Now, what if I were instead measuring the length of a mouse? So, my best drawing of a mouse here draws a little paw, and it kinda looks like a fish with a tail. But let's say that this is a mouse. Would I measure this in meters or centimeters?

Well, a mouse is much smaller in length than a tree is tall, so you would likely measure this in centimeters. A small mouse, I should say, might be maybe 5 or 10 centimeters in length right over here.

Now, let's compare another way or decide another way to think about whether we're measuring in centimeters or meters. Let's say that I went to the local gymnasium, and there's a pool there. There's a pool – that's the water in the pool – and I were to measure the length, and I know it is 25 something. It's either 25 meters or 25 centimeters.

Remember, this is the pool at the gym. Pause this video. Do you think this would be 25 centimeters or 25 meters? Well, as you can imagine, the length of a pool – this tall basketball player – many of them could lie down end to end to get to this length of this pool.

So this would be a 25 meter pool. A 25 centimeter pool – that would be maybe about the size of a cell phone, or maybe smaller or a little bit larger depending on the cell phone that you're talking about. So for a pool, you'd be talking in terms of meters.

What if we had a building of some kind? So this is a building right over here, and let's say it is a three-story – or let's call it it's a four-story building – and someone were to say that it is 15 something tall. Would this be 15 meters tall or 15 centimeters tall?

Well, 15 centimeters – that might be a Lego building. A real building would be 15 meters in this scenario.

Now, what if I were to say the length of my thumb? The length of my thumb right over here – and I know it is 5 something. This length right over here is five something – it's either five meters or five centimeters. Which one do you think it is?

Well, if it was five meters, I would be a very, very, very large giant. My thumb would be twice as tall, or more than twice as tall, as a fairly tall basketball player. So this would be five centimeters right over here.

So hopefully that gives you a sense of meters and centimeters, and on Khan Academy, there's a lot more practice so you can get a little bit more sense of estimating with these or thinking about when one set of one unit or the other is more appropriate.