Lesson video

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Hi everyone, how are you? At the moment I'm feeling a little bit flustered.

After this lesson, I'm heading up to the shops and I'm going to be taking my car, but I cannot find my car key anywhere.

When I was setting up for the lesson, I know I brought my key in with me so that as soon as the lesson is finished, I'll be able to head straight out.

Can I find the key now? No, I can't.

I really hope that worrying about where my key is, isn't going to distract me too much from this lesson.

Hopefully I'll be able to keep on track, put it out of my mind and then deal with finding the key at the end.

If you've got anything that's distracting you right now, then I wonder if you also can park it for the moment.

Maybe moving to a different room, moving away from the distraction so you can focus on your learning with me for the next 20 minutes.

Press pause while you get yourself sorted, then come back and we'll start.

In this lesson, we are converting between millimetres and centimetres.

We're going to start off by having a think about appropriate units of measurement.

Before we spend time exploring centimetres and millimetres, and then connecting them.

That will leave you ready for the independent task at the end of the session.

Things you're going to need a pen or pencil, some paper and a ruler.

A ruler is really important today if you have one.

Press pause while you collect those things, then come back when you're ready.

Let's have a look, shall we? Matching measurements.

In black is an item or a thing being measured.

In pink are the measurements of that item, but I don't think that they're correctly matched at the moment.

For example, the length of a pencil, 30 kilogrammes doesn't sound right.

Press pause.

Can you correctly match up the items with the measurements then come back and we'll check.

You ready to have a look? Let's take away.

Let's remove the measurements and look at the items. The mass of a chocolate bar, what did you get? That's better, isn't it? 48 grammes compared to the mass of a Labrador, 30 kilogrammes.

A big difference there.

But of course there is a chocolate bar compared to a Labrador.

You'd expect there to be a difference in the measurements.

A big difference.

The capacity of a washing up liquid bottle could hold 450 millimetres.

Now I know my washing up liquid bottle at the moment has not got 450 millilitres in it.

It's almost empty and I need to replace it, must remember.

The distance between London and Paris.

It's a lot of kilometres, 344 compared to the length pencil 18 centimetres.

Good work, good starts.

You've correct correctly matched the items with the measurements.

Let's start thinking about and exploring millimetres and centimetres.

Do you have your ruler handy? Could you get it to hands now with some paper and pencil because I would like you to draw a line on your paper that is 100 millimetres long.

Draw the line for me.

I'm going to start drawing mine on the screen.

Now my ruler unfortunately only has centimetres on it.

It doesn't have millimetres.

So already, I'm having to use something that I know about millimetres and centimetres to help me.

I'm going to draw my line, are you ready? So my line that's 100 millimetres long.

I'm drawing up to the 10 because of something I already know about 10 centimetres.

10 centimetres is equal to 100 millimetres.

So if I'm drawing a line that's 100 millimetres long, I can draw a line that's 10 centimetres long.

Hold up your paper, let me see your 10 centimetre long lines.

Let me see your 100 millimetre long lines.

Good work.

Are ready for the next line? So keep your ruler, pencil and paper ready because I'd like you to draw now a line that is 10 millimetres long.

Draw your line for me.

I'm going to get my ruler ready.

Same problem as before, but I'm going to use something I know to draw my line.

Are you ready for me to draw mine? A couple of seconds more.

I'm drawing my line now.

Ready please, here we are.

There's length of my line.

But I haven't drawn up to the 10 because my ruler is only in centimetres.

I've drawn up to the one because 10 millimetres is equal to one centimetre.

Say that whole balanced equation for me.

10 millimetres is equal to one centimetre.

Good, next.

Draw a line that's five millimetres long.

Draw it with your ruler, use your pencil and paper.

Getting mine ready.

How can I use what I know this time? Hold up your paper for me once you've drawn your line.

Let me have a look.

Wow, it's short isn't it? Here is mine.

Really short.

And what have I used to help me here? Five millimetres is equal to or not one centimetre is less than one.

How much of one? Just half of it 0.

5 centimetres, or five tenths of a centimetre.

Ready for the next one? Draw a line that is one millimetre long.

Have you go, I think you'll be quick with this one.

Back already, here is mine.

My ruler, eyes peeled.

Eyes peeled, magnifying glasses out because there is my one millimetre long line.

Now comparing that to one centimetre, how much of one centimetre is it? It's one tenth.


1 of a centimetre really short.

Let's start to get a little bit bigger than.


1 centimetres is equal to one millimetre.

So 0.

2 centimetre.

Draw me a line that 0.

2 centimetre long.

Rulers ready Drawn it? Two tenths of a centimetre is mine.

A little bit more than 0.

1, than one tenth, than one millimetre.

Next, 0.

8 centimetres.

How many millimetres is that going to be? Draw it for me? Rulers handy, lines being drawn.


8 of a centimetre, eight tenths of a centimetre.

How many millimetres? Eight millimetres.

Good work.

Ready for 0.


So a new line that is 0.

9 centimetres long is nine tenths of a centimetre.

How many millimetres is it? Draw it for me.

Hold it up compared to mine.

It's almost a centimetre, isn't it? How many millimetres? Tell me.

Nine millimetres long.

Next one, draw a line that is one centimetre long.

Rulers ready? Join your line.

I'm drawing from zero to one.

Is ten tenths of a centimetre is a whole centimetre? And is how many millimetres? Show me with your fingers? Ten millimetres good.

Final one.

Draw a line that is 1.

1 centimetres long.

So a little bit more than a centimetre.

How much more.

Rulers ready? Draw your line, 1.

1 centimetres.

Here's mine.

It's going to be 11 tenths.

It's ten tenths and one more tenth, 11 tenths long.

How many millimetres is that? Say it, says again.

11 millimetres long.

Take a look now then.

We have drawn all sorts of different lines of different lengths.

And here we've got some connections.

100 millimetres is equal to 10 centimetres.

10 millimetres is equal to one centimetre, and one millimetre is equal to 0.

1 centimetres.

Can you read through the second list working from centimetres to millimetres? Have you go read all of them one at a time.

Good, good and well done.

Now look closely.

What do you notice? Look at the patterns and connections between the numbers.

What are you noticing? Yes, the numbers are getting smaller.

We're moving from 100 to 10.

When we move from millimetres to centimetres, we're moving from 10 to one.

But with centimetres to millimetres, what's happening? The numbers are getting bigger from one to ten, ten to 100, 0.

1 to one.

Can we describe how much bigger or smaller they're getting? We can, good.

Yes, millimetres to centimetres, the numbers are getting smaller, ten times smaller.

How about centimetres to millimetres? They're getting how much bigger? Ten times bigger.

Good, so we could share what we've noticed like this.

When we move from millimetres to centimetres, our numbers get ten times smaller, we divide by 10.

What would it be from centimetres to millimetres? Ten times bigger.

Good, we multiply by 10.

Now I would like you to order these measurements from shortest to largest.

Notice that some are centimetres and some are millimetres.

So a helpful hint for you.

Write each measurement in both centimetres and millimetres.

That's where this page is going to help.

So maybe quickly write down millimetres divided by 10 centimetres and centimetres multiplied by 10 millimetres.

Quickly write that down.

I give you 10 seconds.

Five, four, three, two, one.

Okay, moving on.

I'd like you to pause on this screen.

Order from shortest to largest.

Use the helpful hint.

Come back when you're ready to check.

Should we have a look? I hope you use the hint.

Let's remove that now and let's do it.

Let's make sure we've got all the measurements in centimetres and millimetres.

So anything that's in centimetres that I want to be in millimetres, I multiply by 10.

There we go.

And anything in millimetres that I'd like to have in centimetres, I divide by 10.

There we go.

Now that we've done this, we should be able to order them.

So more accurately and more easily.

Which of them is the shortest? Good, one millimetre.

What's next, good check against yours.

Is this what you had? If it isn't? Why isn't it? Have a think about what you were doing and thinking about instead.

See if you can spot your own mistakes.

Which was next? Good.

Followed by and next, bit louder.

Please I couldn't hear that.

So the next one again, please a bit louder.

That's better and finally.

So we've ordered from shortest to largest.

I wonder if anyone who ordered from largest to shortest by mistake.

I wonder if there's anyone that didn't use the helpful hints that perhaps if they did, would have found the ordering more easy and perhaps they would have had more accuracy.

So, we've ordered from shortest to largest, and we've used what we know about converting between centimetres and millimetres, millimetres and centimetres.

Let's take our learning forward.

Here is a measurement, read it to me.


I would like us to record in centimetres and millimetres like we have, but also only in centimetres or only in millimetres.

So let's use what we know.

Three centimetres as millimetres would be 30 millimetres and four millimetres in centimetres would be 0.

4 centimetre.

Now that I've got these recordings, can I use them to say how much it's worth just as centimetres and how much it's worth just as millimetres.

I think I can.

In centimetres, three and 0.

4, 3.


And just in millimetres 30 and four, 34 millimetres.

You have to try with this one.

Press pause if you'd like to, come back when you're ready to share.

You're ready to take a look.

Let's use what we know.

Five centimetres is how many millimetres? Multiply by 10, 50.

To millimetres or centimetres divide by 10, 0.


So now can we combine a centimetres, what did you get? 5.


And as millimetres, 52.

And look, 52 multiplied by 10.

Sorry, did I say 50? Let me say this again, I can't remember what I said.


2 multiplied by 10 is 52.

52 divided by 10 is 5.


The connections are there.

One more, pause again, have a go.

Ready? What do you know? one centimetre, what do you know? It's 10 millimetres multiply it by 10.

What about eight millimetres? It's 0.

8 centimetres, divided by 10.

Can you combine? What did you get the centimetres? One and 0.

8, 1.


What did you get the millimetres, good 10 and 8, 18.

Look at the connection.

How do we get from centimetres to millimetres? Multiply by 10.

How do you get four millimetres to centimetres, divided by 10.

18 divided by 10, 1.



8 multiplied by 10, 18.

I think you are ready for your task.

I would like you on a piece of paper with a ruler really important to draw your own copy of these straight lines and the triangle and rectangle.

When you've done that, right the measurements of the lines and the perimeters of the shapes in three ways.

In centimetres and millimetres, in centimetres and in millimetres.

So it will look something like this for each of the lines and each of the shapes.

Press pause, have a go at the task and come back when you're ready to share.

How did you get on? Hold on your paper for me? Let me see the drawings.

Let me see the measurements.

Wow, they are busy pieces of paper you've been working really hard.

And I can see next to each line, next to each shape, a value in centimetres and millimetres, just in centimetres and just in millimetres.

We can't go through each of these because the size of your lines and shapes will be different to mine and different to the other person's and anyone else that's been taken part in the activity.

There'll be too many options.

So instead, let's have a look at this activity.

Which has the greater perimeter? the square or the purple shape, the pentagon.

Both of the shapes are regular polygons.

I've only given you one dimension for each shape.

Does that matter? No because they are regular.

So all of the edges are equal.

So that's how many lots of 14 millimetres? Four.

How many lots of 1.

2 centimetres, Five.

Press pause, have a go, see what you think and come back.

Ready? I wonder if anyone converted 1.

2 centimetres into millimetres, multiply by 10, 12 millimetres.

Now I'm comparing 12 and 14.

14 multiplied by four, 12 multiplied by five.

I think that the pentagon is going to have the greater perimeter.

10 times four is 40.

Four times four is 16.

16 and 40 is 56.

12 times five, I know my times table.

My five and my 12 times, 12 fives are 60 So the perimeter of the pentagon is 60 millimetres.

The perimeter of the square is 46 millimetres.

The pentagon has the greater perimeter.

If you would like to share any of your learning from this lesson with Oak National, please ask your parent or carer to share your work on Twitter tagging @OakNational and #LearnwithOak.

Well done everyone, a brilliant lesson.

Thank you for all of your engagement and participation.

It really took my mind off, my missing car key.

But now it is all I can think about again.

Where is my key pardon? Is that what you were trying to tell me earlier? You wanted to share something with me before.

My keys, check my pocket.

My key has been in my pocket this whole time.

Thank you so much.

I'm now set to go.

Enjoy the rest of your day and see you again soon.