Geometry Formulas

Triangle

A = ½ × b × h

P = a + b + c

Heron: A = √(s(s-a)(s-b)(s-c))

s = (a+b+c)/2 (semi-perimeter)

Circle

A = π × r²

C = 2 × π × r

D = 2r

π ≈ 3.14159265

Rectangle

A = l × w

P = 2(l + w)

d = √(l² + w²)

Square

A = a²

P = 4a

d = a√2

Trapezoid

A = ½(a + b) × h

P = a + b + c + d

Regular Polygon (n sides)

A = (n × s² × cot(π/n)) / 4

P = n × s

Sphere

V = (4/3)πr³

SA = 4πr²

Cylinder

V = πr²h

SA = 2πr(r + h)

Cone

V = (1/3)πr²h

SA = πr(r + l)

l = slant height = √(r²+h²)

Rectangular Box

V = l × w × h

SA = 2(lw + lh + wh)

Quick Calculator — Circle

Radius

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Area

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Circumference

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Diameter