Geometry Lab reference
Area & perimeter
The space inside is different from the distance around.
Rectangle: A = wh · P = 2(w + h)
The idea
Area measures a flat region in square units, such as cm². Perimeter measures the length of its boundary, such as cm. For a circle, the perimeter is called the circumference: C = 2πr, while area is A = πr².
Work through an example
An 8 cm by 5 cm rectangle has area 40 cm² and perimeter 26 cm. A 10 cm by 4 cm rectangle also has area 40 cm², but its perimeter is 28 cm. Equal areas do not imply equal perimeters.
What to watch for
For a triangle, A = ½bh uses the perpendicular height, not necessarily a sloping side. Convert measurements into the same unit before combining them.
Make the formula move.
Explore this idea with real inputs.