Perimeter
Perimeter is the total distance around the boundary of a polygon in Grade 8 math (Yoshiwara Core Math). Add all side lengths to find it. For a rectangle with length l and width w: P = 2l + 2w. For a square with side s: P = 4s. Irregular polygons require summing all individual sides. Perimeter is measured in linear units (cm, m, ft) and differs fundamentally from area. Real-world applications include fencing, picture frame molding, and running tracks — any context involving the outer boundary of a shape.
Key Concepts
Property In mathematics, the perimeter means the length of the boundary of a region. To find the perimeter of a straight sided figure, measure the length of each side and add up the lengths of the sides.
Examples A rectangular garden is 10 meters long and 7 meters wide. Its perimeter is the sum of all its sides: $10 + 7 + 10 + 7 = 34$ meters. A triangular park has sides measuring 50 feet, 60 feet, and 75 feet. The perimeter is found by adding these lengths: $50 + 60 + 75 = 185$ feet. For a square window with one side measuring 2 feet, the perimeter is $4 \times 2 = 8$ feet, since all four sides are equal.
Explanation Imagine you are an ant walking around the edge of a shape. The total distance you walk in one full circuit is its perimeter. It measures the length of the boundary, not the space inside.
Common Questions
What is perimeter and how is it calculated?
Perimeter is the total length around the outside of a shape. Add all side lengths together.
What is the formula for the perimeter of a rectangle?
P = 2l + 2w. A 6 cm × 4 cm rectangle has perimeter 2(6) + 2(4) = 20 cm.
What is the formula for the perimeter of a square?
P = 4s, where s is the side length.
What units are used for perimeter?
Linear units: cm, m, inches, feet — the same unit as the side lengths.
How is perimeter different from area?
Perimeter is the distance around a shape (linear units). Area measures enclosed space (square units).