formula for sq in of pizza

guys i forgot how to figure this

Pi * Radius squared

try this
http://math.about.com/library/blcirclecalculator.htm

Calculating the area of a pizza

for detailed PI, to 6 digits, it is 3.141593
Radius is half the diameter (16" pizza diameter has an 8" radius)

3.141593 * 8*8 = 201.0619 square inches. et cetera

I put this is for anyone doing a search many moons later.