Draw the figure on your paper. Label the dimensions. For a circle you'll need a radius. For the rectangle, parallelogram and triangle, you'll need a base and height, sometimes called length and width. Since a square is the same on all sides, you only need one measurement.
Choose the correct formula for your geometric figure.
Area of Circle = pi * Radius^2
Area of Square = Side * Side
Area of Rectangle = Length * Width
Area of Parallelogram = Base * Height
Area of Triangle = 1/2 * Base * Height
Plug your dimensions into the right formula. Because all of these formulas have two dimensions multiplied together, area is measured in square dimensions, such as square feet or square inches. For example, if you have a rectangular room that measures 12 feet by 11 feet, the area is 132 square feet.