# π (Pi) Definition

This figure illustrates the definition of (pi) in terms of the circumference and diamater of the circle.

**Note:**This website uses the constant (tau) instead of (pi) as the default circle constant. The substitution can be used to translate between the two constants.

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The circle constant τ (tau) is a geometric constant approximately equal to 6.283. The numeric value is defined as the length of any circle's circumference divided by the length of its radius.

The greek letter π (pi) is a geometric constant approximately equal to 3.1416. Its value is equal to the length of any circle's circumference divided by its diameter.