wikiHow Triangle Perimeter Calculator To find the perimeter of a triangle, you need to add the lengths of all three sides. Here are the steps to find the perimeter of a triangle using a calculator: 1. Enter the length of the first side into your calculator. 2. Enter the length of the second side into your calculator. 3. Enter the length of the third side into your calculator. 4. Add the lengths of all three sides together. For example, let's say you have a triangle with a first side measuring 4 cm, a second side measuring 6 cm, and a third side measuring 8 cm. To find the perimeter of this triangle, you would follow these steps: 1. Enter 4 into your calculator. 2. Enter 6 into your calculator. 3. Enter 8 into your calculator. 4. Add the lengths of all three sides together: 4 + 6 + 8 = 18. So the perimeter of the triangle is 18 centimeters. Page