Look at this rectangle on the board. Six squares along, four squares up. How many small squares are inside altogether? Hands up: what is the quickest way to count them?

Watch carefully as we measure the area of three rectangles by counting the unit squares each one covers. Each square is one centimetre wide and one centimetre tall, so we count in square centimetres (cm²).

Example 1: 6 × 4 = 24 cm²

Six squares along the length, four squares up the width. Count the rows of six together: 6, 12, 18, 24. The rectangle covers 24 square centimetres.

Example 2: 5 × 5 = 25 cm²

The length and width are equal, so the rectangle is also a square. Five rows of five: 5, 10, 15, 20, 25.

Example 3: 8 × 3 = 24 cm²

A long thin rectangle, eight along by three up. Three rows of eight: 8, 16, 24. Notice anything? Same area as Example 1, but a different shape.

Now look at this rectangle: twelve squares along, seven squares up. Count those one at a time and we would be here all afternoon. Watch as we use a faster way — multiply length by width.

Now we work three rectangles together as a class. One pupil at a time comes up to the board: drag the corners to set the dimensions, then read the area off the readout. Everyone else watches, works the multiplication in your head, and calls out to agree or correct each answer before we move on.