Perimeter

Hello, and welcome to Myriora Maths! An ant walks all the way round the edge of a field. How far does it walk? That distance is called the perimeter. Let's find it.

The perimeter is the distance all the way round a shape. For this rectangle, add up all four sides: six, add four, add six, add four. That's twenty centimetres.

A rectangle has two lengths and two widths. So add one length and one width, then double it. Six add four is ten, doubled is twenty.

Some shapes have missing sides. In this L shape, the long bottom is ten. The two short top edges must add up to ten as well. And the two right-hand edges must add up to the full height, eight.

So the perimeter is ten add ten across, and eight add eight up and down. That's thirty-six centimetres.

Let's try one together. A square has sides of five centimetres. What is its perimeter? Say it out loud!

Four sides of five centimetres: twenty centimetres!

Here's a question that catches lots of people. What is the perimeter of this rectangle, drawn on squares? Some people count all the squares inside. But that's the area! The perimeter is only the edge: walk round it, and count the sides.

Your turn! A rectangle is seven centimetres long and three centimetres wide. What is its perimeter? Pick the right card. You've got twenty seconds, or pause the video. Go!

Time's up! Seven add three is ten. Double it: twenty centimetres!

Quick review. The perimeter is the distance all the way round. For a rectangle, add the length and width, then double. For other shapes, find any missing sides first. And don't count the squares inside: that's area. See you next time!