How to Use PI for Circle Calculations in Excel

PI() returns π to 15 digits — use it for areas and to find out which pizza size is really the best value.

You will learn to

• Calculate a circle’s area from its diameter
• Calculate price per square inch
• Find the best value across sizes in one formula

How it works

PI() returns π accurate to 15 digits (3.14159265358979). It takes no arguments but still needs its parentheses — typing =PI without them returns #NAME?. A circle’s area is =PI()*r^2, and since menus list diameters, use =PI()*(diameter/2)^2.

Area grows with the square of the diameter, which is why bigger sizes are usually much better value. Divide price by area to get a price per square inch, then use MIN across sizes to find the best deal.

=PI()*(B2/2)^2