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need to convert 8'' inside diameter to sq in?

[JohnS]

Originally Posted by connolly

need to convert 8'' inside diameter to sq in?

area of a circle is pi*R² or (pi/4)*D², (radius is half the diameter)
3.14159*4*4 = 50.3 in²

pi is irrational (has an infinite number of decimal digits), so you have to decide where to round off, above is plenty accurate for most purposes.