Add up the lengths of all the sides. Since there are two pair of equal sides, just take each the length and double it and then the width and double it. Now add those two numbers. If the length is L and the width is W, the perimeter is 2L +2W
Chat with our AI personalities
In order to find the perimeter of a 3D rectangle you must gather the lengths of the known sides, calculate the missing rectangular values, and use the formula for perimeter.
I believe you've already found it.
When you think about it for a while, they're really NOT different. The rectangle formula needs a bit more detail, because its sides don't all have the same length, so its length and its width have to be handled separately. But the rectangle formula works perfectly well if you use it to find the perimeter of a square.
Height = (Perimeter/2) - Base
The perimeter of a rectangle = 2 x (length + width) = 2 x (12 + 8) = 2 x 20 = 40 inches