Circumference of Circle Formula
The circumference of a circle is given by the constant (tau) multiplied by the radius of the circle, where and .
Variable  Description 

Circumference of the circle  
The circle constant (tau), where  
The radius of the circle 
The circumference of a circle is given by the constant (tau) multiplied by the radius of the circle. For example, to find the circumference of a circle with a radius of length 3 the formula is:
To calculate the circumference of a circle with a radius of length one, shown in the image above, multiply the circle constant (tau) by the value of the radius.

Set up the formula and substitute the value for into the formula.

Evaluate multiplied by .

The circumference of the circle is approximately 6.28318530718 units.
To calculate the circumference of a circle multiply the radius by the constant (tau) to get the result.

Set up the formula and substitute the value for into the formula.

Evaluate multiplied by .

The circumference of the circle is approximately 12.566 units.
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.