Area is a size measurement of a specific region and is expressed in square units such as square meters or square kilometers. Calculating the area of a space is an important for everyday activities, including estimating the amount of carpet for a bedroom or landscaping a yard. The formula for calculating the area of a rectangle is slightly different from the formula used to calculate the area of a circle or triangle.
Things You'll Need
 Calculator
 Tape measure
Area of a rectangle

Measure the length of the rectangle.

Measure the width of the rectangle.

Multiply the length of the rectangle by the width of the rectangle to obtain the area. Ensure the units used for the length and the width are the same. The resulting value will be the units squared.
Area of a circle

Determine the radius of the circle.

Square the radius by multiplying it by itself. The resulting value will be the units squared.

Multiply the value by pi, which is 3.1415927. You now have the area.
Area of a Triangle

Measure the length of the base of the triangle.

Measure the height of the triangle.

Multiply the base by the height. Ensure the units used for the base and the height are the same.

Divide the value by two to obtain the area of a triangle. The resulting value will be the units squared.
Tips & Warnings
 When determining the area of a section that is not a perfect square, it is useful to divide the area up into a series of smaller sections and then add them all together.
References
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