Area Formulas

Area Formulas

Square = a ² 
Rectangle = ab 
Parallelogram = bh 
Trapezoid = h/2 (b₁ + b₂) 
Circle = pi r ² 
Ellipse = pi r₁ r₂ 

triangle =

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

   Units

Area is measured in "square" units. The area of a figure is the number of squares required to cover it completely, like tiles on a floor.

Area of a square = side times side. Since each side of a square is the same, it can simply be the length of one side squared.

If a square has one side of 4 inches, the area would be 4 inches times 4 inches, or 16 square inches. (Square inches can also be written in².)

Be sure to use the same units for all measurements. You cannot multiply feet times inches, it doesn't make a square measurement.