Math Lab
← All labs

Perimeter of a Rectangle

Perimeter · Class III

Choose length and width; walk all four sides.

6 u
type a value
120
4 u
type a value
120
Live values
  • Perimeter20
  • All four sides20
xy
  • Perimeter as width varies

Formulas in this lab

  • Perimeter
    2(l+w)2(l+w)
  • All four sides
    l+w+l+wl+w+l+w
Tip: Perimeter grows in a straight line with width; slope is 2 because two sides of length w appear.

Frequently asked questions

▶What is perimeter?

Perimeter is the total distance around the edge of a shape. For a rectangle with length 5 and width 3, you walk 5 plus 3 plus 5 plus 3, which is 16. So the perimeter is 16 units.

▶How do I use the perimeter lab?

Choose the length and width of a rectangle with sliders. The lab draws the rectangle, walks around it edge by edge, and adds the sides. The total is the perimeter.

▶When do we use perimeter?

When putting a fence around a garden, you measure the perimeter to know how much wire to buy. Sticking a border on a chart paper for a project also needs the perimeter.

▶Easy formula for rectangles

Perimeter of a rectangle equals 2 times (length plus width). So a 6 by 4 rectangle has perimeter 2 times 10, which is 20. This shortcut saves time once you understand why it works.