# Lesson Video: Choosing Grams or Kilograms Mathematics • 3rd Grade

In this video, we will learn how to choose between grams and kilograms to measure the weight of an object in.

11:08

### Video Transcript

Choosing Grams or Kilograms

In this video, we’re going to learn how to choose between grams and kilograms to measure the mass of an object. When we’re measuring the mass of an object, it’s a way of finding out how heavy the object is. If we look at the picture, the girl has asked the boy, how heavy the cat is, and he’s given the answer, six. What would you say if someone said that to you? You’d probably say, six what?

When we measure things, we don’t just give a number. We also have a unit of measurement. This is the thing that we’re measuring in. And the two units of measurement that we use to measure mass, and these are the two that we’re going to be thinking about in this video, are what we call grams and also kilograms.

We’re gonna come back to the cat in a moment. But for now, let’s find out some more about grams and kilograms. If something’s measured in grams, we don’t always write the whole word out. Most often, you’ll see just the letter g. This stands for grams. Have you got an idea how heavy one gram is? Let’s go through some objects that have a mass of about one gram. This should help you to picture how heavy one gram is.

First of all, can you picture a ballpoint pen? Yes. Well, if you take the lid off that ballpoint pen, the lid weighs about the same as one gram. You know the sort of pin that you might use to push things into a notice board with. You might call this a thumbtack or a drawing pin. These weigh about the same as a gram, so does one paperclip. And can you picture a packet of chewing gum? Well, if we took out one of the sticks of chewing gum, that weighs about one gram too. Hopefully, this gives you some idea of how heavy one gram is.

Just like with the gram, if we measure mass using kilograms, we don’t always write the whole word out. We often just see the letters kg, kilograms. But do you have any idea what a kilogram is like? Often the packets of rice or sugar that we might find in our kitchen cupboards are one kilogram. A pineapple is about the same as a kilogram. Have you ever seen those thick dictionaries you can get? Well, a really thick hardback book like this might weigh one kilogram. And a liter of water weighs one kilogram too. Hopefully these objects give you some idea of what grams and kilograms weigh.

What would you say about these two units of measurement if you had to compare them? Well, if we look at all the objects that weigh about the same as one kilogram, these seem to be a lot heavier than those that weigh about the same as a gram. So we could say one gram is lighter than one kilogram. It’s a lot lighter, isn’t it? I think I know which you choose if you were told you had to balance a paperclip or a pineapple in your head. One kilogram is a lot heavier than one gram. But you know, we often have to choose which unit of measurement we’re going to use.

Let’s come back to our cat from earlier on. If we were going to measure the mass of a cat, do you think it’s best to measure it in grams or kilograms? Remember, one gram is about the same as a paperclip. Now, if we had to count how many paperclips weighed about the same as a cat, we’d need a huge amount of paperclips. A cat is going to weigh a large number of grams. Now we said kilograms are about the same as a bag of rice. How many bags of rice do you think a cat weighs? Our cat looks quite big, doesn’t it? What do you think, maybe four, five bags of rice? Although we can measure the mass of a cat in both grams or kilograms, it’s better to choose kilograms to measure heavier objects like cats.

What about this pair of glasses? Shall we use grams or kilograms? If we imagine how much a pair of glasses weighs, we know that it’s going to be less than one kilogram. Imagine wearing a pair of glasses that were the same as balancing a pineapple on the end of your nose. They’d be really heavy, wouldn’t they? So we know that the mass of a pair of glasses is going to be less than one kilogram. The best unit of measurement to measure light objects like a pair of glasses is grams. It’s quite tricky to make the right decision. But let’s try answering some questions now where we have to choose between kilograms and grams.

True or False: If we measure the mass of lighter objects, it is better to use kilograms than grams.

When we measure the mass of an object, we’re trying to find out how heavy it is. And in our question, we can see two units of measurement that we can use to weigh objects. Can you see them? There’s kilograms, which we often write kg, and grams, for which we often write g. Now, we could use these units of measurement to weigh anything, but it’s not always a good idea. Sometimes it’s better to use one unit of measurement than the other. And this question is asking us about lighter objects. If we’re measuring the mass of lighter objects, is it better to use kilograms or grams?

What do you think we mean by lighter objects? A feather is a light object. This pen is a light object. You could probably say a carrot is a light object too. It’s not heavy, is it? If an object is light, it’s not heavy. Now, if we wanted to measure the mass of these light objects, is it better to use kilograms or grams? To help us understand, we need to remind ourselves how heavy one kilogram and one gram are. One kilogram weighs about the same as a bag of rice. And one gram weighs about the same as the lid of a ballpoint pen.

Now, which unit of measurement do you think it makes sense to measure these light objects with? Would you weigh how heavy they are in bags of rice or in pen lids? If we had a set of scales, we put a bag of rice on one end and one of our light objects on the other, it would come crashing down. A kilogram is much heavier than our light objects. It would be much easier to see how many pen lids weighed the same as a carrot. Grams are generally better for weighing lighter objects and kilograms for weighing heavier objects.

Now, our sentence says, if we measure the mass of lighter objects, it’s better to use kilograms than grams. Well, we’ve just said this isn’t true, is it? The statement is false. Let’s say it the correct way round just to end with. If we measure the mass of lighter objects, it is better to use grams than kilograms.

What is the mass of the leaf? One gram or one kilogram.

Our question asks us what the mass of the leaf is. In other words, how heavy is it? Now, if the question just asked us this and didn’t give us any clues, then we might find it quite difficult to answer. But we can see at the bottom we’ve got two answers to choose from, which makes it easier for us. Both our answers have the number one in front of them. The mass of the leaf is one something. But is it one gram or one kilogram? We need to choose the correct unit of measurement.

To help us, let’s remind ourselves of some objects that weigh about the same as one gram and one kilogram. One gram is about the same as a stick of chewing gum. And a large dictionary is about the same as one kilogram. Now, we’ve thought about these everyday objects. It can help us think about the mass of the leaf. We can see straight away, can’t we, that one gram is quite light. And although one kilogram isn’t really, really heavy, it’s still a lot heavier than a gram.

So what do you think, is the mass of the leaf more likely to be the same as a stick of chewing gum or a big dictionary? It’s more likely to weigh one gram, isn’t it? Think about the way that leaves fall from the tree slowly and get blown around by the wind. We can pick lots and lots of them up in our hands, and it doesn’t feel heavy at all. A leaf is very light, and so we know the mass of the leaf is one gram.

Which unit is best to measure the mass of a child? Kilograms or grams.

If we’re measuring the mass of a child, we’re finding out how heavy they are. We’re given two units of measurement to choose from. We could find out how heavy they weigh in kilograms, but we also could in grams. The question asks us which unit is best because one makes a bit more sense than the other. A kilogram is about the same as a bag of apples or a liter of water. A gram is about the same as a paperclip.

Now imagine a child stands on one end of a set of weighing scales. What would you rather use to get the scales to balance? A few bottles of water or bags of apples or some paperclips? Well, we said some paperclips, you’d need lots and lots and lots and lots of paperclips, wouldn’t you? Almost too many to count. The number of grams that a child weighs is a big number. We usually use kilograms for measuring heavier objects. And so the best unit to use to measure the mass of a child is kilograms.

So what’ve we learned in this video? We’ve learned how to choose between grams and kilograms to measure the mass of an object.