If you know the volume and height of the prism, then you can divide the volume by the height to get the base area. B=V/H. If you know the side lengths of the base then you could simply multiply them together to get the base area.

SamSenner

The perimeter of the base would be the perimeter for the circle. C= 2πr
c is circumference (perimeter), π is 3.14, and r is radius( half the diameter)