Triangle
Area = ½ × b × h
b = base
h = vertical height

Heron's Formula
You can calculate the area of a triangle if you know the lengths of all three sides

Step 1: Calculate "s" (half of the triangles perimeter):

Step 2: Then calculate the Area:

SAS Triangle Area

When you know the lengths of two of a triangle's sides plus the measure of the angle between those sides (SAS), you can find the area of the triangle. Suppose in this triangle (not necessarily a right triangle), angle C has 2 sides a and b, then the area of the triangle will be

Area of triangle = 1/2 * a * b * sin(C) 

Circle

Area = pi * square of radius

Rectangle
Area = w × h
w = width
h = height

Trapezoid
Area = ½(a+b) × h
a, b are the 2 parallel sides
h = vertical height

Ellipse
Area = πab
a, b are the 2 axis values

Square
Area = a2
a = length of side
Parallelogram
Area = b × h
b = base
h = vertical height

Area = π × r2
Circumference = 2 × π × r
r = radius

Sector
Area = ½ × r2 × θ
r = radius
θ = angle in radians