## Summary

To calculate the circumference of a circle, you can use the PI function. In the example shown, the formula in C5 is:

``2*PI()*B5``

As the formula is copied down, it calculates the circumference of a circle for each radius given in column B.

## Generic formula

``=2*PI()*A1``

## Explanation

In geometry, the circumference of a circle with radius (r) is defined by the following formula: =2πr` `

The Greek letter π ("pi") represents the ratio of the circumference of a circle to its diameter. In Excel, π is represented in a formula with the PI function, which returns the number 3.14159265358979, accurate to 15 digits.

``````=PI() // returns 3.14159265358979
``````

Therefore, the formula to calculate the circumference of a circle with a radius of 3 is:

``````=2*PI()*3 // returns 18.85
``````

And the formula to calculate circumference based on the radius values in column B, is:

``````=2*PI()*B5
``````

Author

### Dave Bruns

Hi - I'm Dave Bruns, and I run Exceljet with my wife, Lisa. Our goal is to help you work faster in Excel. We create short videos, and clear examples of formulas, functions, pivot tables, conditional formatting, and charts.