Perimeter Formulas for Common 2D Shapes

Direct answer

What is a perimeter formula?

Perimeter formulas calculate the distance around a 2D shape. For polygons, perimeter usually adds side lengths, such as triangle perimeter $P = a + b + c$ or rectangle perimeter $P = 2 (l + w)$ . For circles, perimeter is circumference: $C = 2 π r = π d$ .

Quick table

Perimeter formulas table

Shape	Formula	Use
Square	$P = 4 s$	s = side length
Rectangle	$P = 2 (l + w)$	l = length, w = width
Triangle	$P = a + b + c$	a, b, c = side lengths
Circle	$C = 2 π r = π d$	r = radius, d = diameter
Parallelogram	$P = 2 (a + b)$	a and b = adjacent sides
Rhombus	$P = 4 s$	s = side length
Regular polygon	$P = n s$	n = number of sides, s = side length

Formula cards

Quick formula cards

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Circle Formulas

Area $A = π r^{2}$

Circumference $C = 2 π r = π d$

Diameter $d = 2 r$

Radius $r = \frac{d}{2}$

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Triangle Formulas

Area $A = \frac{1}{2} bh$

Perimeter $P = a + b + c$

Right triangle $a^{2} + b^{2} = c^{2}$

Heron's formula $A = s (s - a) (s - b) (s - c)$

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Cylinder Formulas

Volume $V = π r^{2} h$

Lateral surface area $L S A = 2 π r h$

Total surface area $T S A = 2 π r (r + h)$

Base area $B = π r^{2}$

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Cone Formulas

Volume $V = \frac{1}{3} π r^{2} h$

Lateral surface area $L S A = π r l$

Total surface area $T S A = π r (r + l)$

Slant height $l = r^{2} + h^{2}$

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Sphere Formulas

Volume $V = \frac{4}{3} π r^{3}$

Surface area $S A = 4 π r^{2}$

Diameter $d = 2 r$

Radius $r = \frac{d}{2}$

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Examples

Step-by-step examples

Rectangle perimeter

Given l = 9 cm and w = 5 cm.
Use $P = 2 (l + w)$ .
$P = 2 (9 + 5) = 28 c m$ .

Triangle perimeter

Given sides 4 m, 6 m, and 8 m.
Use $P = a + b + c$ .
$P = 4 + 6 + 8 = 18 m$ .

Circle circumference

Given d = 12 in.
Use $C = π d$ .
$C = 12 π \approx 37.70 in$ .

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FAQ

Perimeter Formulas FAQ

What is perimeter?

Perimeter is the total distance around the outside of a polygon.

Is circumference the same as perimeter?

Circumference is the perimeter of a circle.

What units does perimeter use?

Perimeter uses linear units such as cm, m, in, or ft.