For finding out triangle's perimeter it is necessary to know length of it's legs. If you know those lengths you need just sum them up and you will gain the perimeter.
For more detailed examination of triangle's perimeter let's look at the example below:
We have a triangle with legs a, b and c (see picture above). Leg a = 2, leg b = 4, leg c = 5. For calculating of triangle's perimeter you have to sum all it's legs up.
P = a + b + c
where P  perimeter; a,b,c – triangle's legs. Thereby, solution of this exercise will be the next:
P = 2 + 4 + 5 = 11
Perimeter of the triangle 
