Area Formulas

Area Formulas

Note: "ab" means "a" multiplied by "b". "a²" means "a squared", which is the same as "a" times "a".

Be careful!! Units count. Use the same units for all measurements. Examples

square = a ²
rectangle = ab
parallelogram = bh 

trapezoid = h/2 (b₁ + b₂)
circle = pi r ²
ellipse = pi r₁ r₂
 

triangle =1/2(bh

one half times the base length times the height of the triangle

  

equilateral triangle =

 
triangle given SAS (two sides and the opposite angle)
= (1/2) a b sin C
triangle given a,b,c = [s(s-a)(s-b)(s-c)] when s = (a+b+c)/2 (Heron's formula)
regular polygon = (1/2) n sin(360°/n) S²
   when n = # of sides and S = length from center to a corner