The circle constant (tau) is a geometric constant that appears in numerous math formulas relating to circles and angles. The numeric value of is defined as the length of the circumference of a circle divided by the length of its radius and is approximately equal to ^{[1]}.
In the radian angle system the circle constant is equal to a full rotation in radains. Measured angles are represented as fractions of the circle constant . For example, shown below are two angles measured using the circle constant.
Here are some traditional geometric formulas in terms of the circle constant.
Calculate the area of a circle given the radius.
Calculate the circumference of a circle given the radius.
Caclulate the volume of a sphere given the radius.
Caclulate the volume of a cylinder given the radius and height.
The circle constant also appears in advanced applications such as the normal distribution, fourier transform, and more.
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.
Radians are a unit that measure angle using the radius of a circle. One radian is equal to the amount of rotation required to travel the length of one radius along the circumference of the circle.
The normal distribution is a continuous probability distribution that appears naturally in applications of statistics and probability. The shape of the normal distribution forms a "bellcurve".

Approximate the Circle ConstantWumbo (internal)

No, really, pi is wrong: The Tau ManifestoMichael Hartl