Trade Math · Perimeter
Perimeter of shapes and objects
Perimeter is the distance around the outside of a shape. It's how you order baseboard, fencing, pipe to trim a room. Easier than area — no multiplication of dimensions — but the quick-glance mistakes are expensive.
Cheat sheet
- Rectangle: P = 2(L + W) — or just add all four sides.
- Triangle: P = side1 + side2 + side3
- Regular polygon (all sides equal): P = number of sides × side length
- Circle (circumference): C = 2 × π × r or π × d (π ≈ 3.14)
- Composite / irregular: add every segment of the outer boundary — don't skip the short ones.
Sign in to keep reading
The rest of the perimeter guide is free — after a quick sign-in
Worked examples, the interactive element, and the practice quiz are available to anyone with a free account. Email magic link, no password. Takes about 30 seconds.
No credit card. The diagnostic is free and so is this guide — we just ask for your email so we can save your progress.