(pi = 
= 3.141592…)
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.
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
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.
The area of a rectangle is the length on the side times the width. If the width is 4 inches and the length is 6 feet, what is the area?
NOT CORRECT …. 4 times 6 = 24
CORRECT…. 4 inches is the same as 1/3 feet. Area is 1/3 feet times 6 feet = 2 square feet. (or 2 sq. ft., or 2 ft2).
It Figures 