What's the perimeter of a square with a side measurement of 6in

To find the perimeter of any figure, simply add the sides. A square has 4 equal sides. 
s + s + s + s = perimeter
Since the sides are equal, we can do this:
4s = perimeter
Now substitute the side length.
4(6) = perimeter
24 = perimeter

The perimeter of a square with a side measurement of 6 inches is 24 inches.

Hope this helps =)