Picture a square that measures one metre along every side. Hands up: how many centimetres run along just one edge of it?

Now the harder question, hold it in your head before anyone answers: how many little one-centimetre squares would it take to cover the whole big square?

Look at the one-metre square with its grid. Notice how the grid splits each edge, so the whole square is filled with rows and rows of one-centimetre squares.

Count with the grid: how many squares in one row, and how many rows? Notice the answer is not the same as one edge count. Look at what the two counts do together.

Now look at two square metres side by side. If one whole holds that many, two wholes hold twice as many.

On screen is the conversion ladder for the edges.

Try it together: set the ladder to 1 m and watch it become 100 cm, then send 100 cm back up to 1 m. Once we can all see the edge scales by 100, we will use that to work out the area next.

First, use the ladder to convert some everyday classroom lengths, each one a step harder: 4.2 m into cm, then 250 cm into m, then 3.5 m into cm.