How to Find the Length of a Triangle With the Addition Method

Add the lengths of each side of a triangle together to calculate the triangle's perimeter.

A triangle is defined as a closed figure with three sides. The length of all three sides of a triangle added together is called the perimeter. You can calculate the perimeter (P) of a triangle using addition if you know the lengths of each side (a, b and c). The formula for calculating the perimeter of a triangle is therefore P = a + b + c.

Things You'll Need

• Ruler

Instructions

1. Measure each side of the triangle. Label each side of the triangle with that side's measurement.

2. Add the lengths of the three sides. Add side a, plus side b, plus side c.

3. The sum of the three sides is the perimeter of, or length around, the triangle.

Tips & Warnings

• If you only know the value of one side of a triangle, you can use more complex formulas to calculate perimeter if you know what type of triangle it is. For instance, an equilateral triangle has three equal sides. If you know the length of at least one side of an equilateral triangle, multiply the known length by three to calculate the perimeter.

References

• The Definition of a Triangle
• G S Rehill's Interactive Math Series: Perimeter of a Triangle

Resources

• The Definition of a Triangle