<P> The symbol used by mathematicians to represent the ratio of a circle's circumference to its diameter is the lowercase Greek letter π, sometimes spelled out as pi, and derived from the first letter of the Greek word perimetros, meaning circumference . In English, π is pronounced as "pie" (/ paɪ /, paɪ). In mathematical use, the lowercase letter π (or π in sans - serif font) is distinguished from its capitalized and enlarged counterpart ∏, which denotes a product of a sequence, analogous to how ∑ denotes summation . </P> <P> The choice of the symbol π is discussed in the section Adoption of the symbol π . </P> <P> π is commonly defined as the ratio of a circle's circumference C to its diameter d: </P> <Dl> <Dd> π = C d (\ displaystyle \ pi = (\ frac (C) (d))) </Dd> </Dl>

The value of pi can be found as