 What you need to know

Things to remember:

– We can draw a diagram to see how we need to multiply and divide.

There are two important facts that we need to remember

There are 100 centimetres in 1 metre

There are 10 millimetres in 1 centimetre.

Out of these, metres are biggest measurement, and millimetres are the smallest.

Writing these words out can be time consuming, so we write them in shorthand:

Metres       —          m

Centimetres      —      cm

Millimetres       —       mm

What is 4m in cm?

We know that 1m is the same as 100cm, and that 4m is just 4 lots of 1m, so we need 4 lots of 100.

$$4\times100=400$$

4m = 400cm

So really, all we did was multiply by 100 to turn metres into cm!

What is 3cm in mm?

We know that 1cm is the same as 10mm, and that 3m is just 3 lots of 1cm, so we need 3 lots of 10.

$$3\times10=30$$

3cm = 30mm

So really, all we did was multiply by 10 to turn cm into mm!

We can draw a little diagram to help us remember which to do. Looking at this, how do you think we might turn mm into cm, or cm into m? What is the opposite of multiplication? Division! So, we can go backwards by dividing. What is 600cm in metres?

To go from cm to m we have to divide by 100.

$$600\div100=6$$

600cm = 6m

Example Questions

We don’t actually know how to do this, but if we look at our diagram above, we can do it in two steps.

Step 1: Convert the metres into centimetres.

$$5\times100=500$$

5m = 500cm

Step 2: Convert the centimetres into millimetres.

$$500\times10=5000$$

500cm = 5000mm

5m = 5000mm

We don’t actually know how to do this, but if we look at our diagram above, we can do it in two steps.

Step 1: Convert the millimetres into centimetres.

$$1000\div10=100$$

1000mm = 100cm

Step 2: Convert the centimetres into metres.

$$100\div100=1$$

100cm = 1m

1000mm = 1m