How to Calculate Area and Perimeter

Knowing how to calculate the perimeter and area of geometric figures will help you in school and in life.
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Different shapes require different methods to figure things out about them. Calculating the area and perimeter of a triangle as well as rectangle will help you figure out how to calculate the perimeter and area of just about any other shape, once you have mastered the skills for calculating the perimeter and area. To calculate the perimeter, you use addition; to calculate the area, you use multiplication.

    Determine the perimeter of a triangle or rectangle by knowing the length of all of the sides of the figure and then adding these numbers together. The perimeter is the sum of all sides of a figure to get one length. So, to find the perimeter, the formula is base + height + base + height. If the base is 10 inches and the height is 5 inches, you would have: Perimeter: 10 + 5 + 10 + 5 = 30 inches.

    Determine the area of a rectangle by using multiplication. To come up with the total area of a rectangle, you need to know the length and width of the rectangle. Then, multiply the length times the width, which will provide you with the total area in square units and denoted as units squared such as miles or inches. So, the formula for calculating the area is base x height. So, if the base is 10 inches and the height is 5 inches, the area equals base x height or 10 inches x 5 inches, which equals 50 square inches.

    Determine the area of a triangle by knowing the height of the triangle and the length of the base. In a right triangle, the height and base are the lengths of the two legs that make up the right angle. Once you have the height and the base, the formula for the area of a triangle is simply 1/2 x base x height.

    Use these calculations to find the area of any figure that has straight sides. Simply break up the figure into rectangles and triangles, determine the area of each and then add them together.


    • You can also figure perimeter by adding the base and height and then multiplying by 2.