Using Segments to Find Perimeter

The perimeter is the distance around a two-dimensional shape. (A rectangle is shown with the edges highlighted.)

To measure, use the straight side of a small square or cube. These are called unit segments.

Place your units one by one around the sides of your rectangle. (Small squares are placed around the edge of the rectangle.)

When you place each unit, don’t leave an extra space between each one. They need to be nice and snug! But be careful they don’t overlap, either. Continue placing your units all the way around.

You’re ready to find the perimeter by counting each side of the units that touch the rectangle.

The units at each corner do not have a segment touching the rectangle, so they aren’t counted.

Count up the unit segments that touch the rectangle. That total is the perimeter! (Numbers 1-18 are placed on each of the squares.) Finding the perimeter of a rectangle is a piece of cake!

Hmm…what would this rectangle’s perimeter be? (A rectangle-shaped cake is shown.)