PI() in Excel: How to Use and Apply π in Your Formulas

If you've ever needed to calculate the area of a circle or work with trigonometric formulas in Excel, you've probably wondered how to get π (pi) into your spreadsheet. Manually typing 3.14159… works, but it lacks the precision Excel can provide.

In this article, I'll show you something about pi in Excel, and we will do a bit of a math refresher. To keep learning more Excel functions, enroll in our Advanced Excel Functions course.

Understanding the Excel PI() Function

The PI() function is Excel’s built-in way of returning the value of the mathematical constant π, which is approximately 3.14159. Pi is fundamental in calculations involving circles and spheres, but it shows up in many unexpected places, also, which I'll show through some examples.

What does the PI() function do?

You might be wondering what sets PI() apart from simply typing 3.14 into a cell. The answer is precision. When you use PI(), Excel returns π to 15 significant digits, which is more than enough for almost any calculation you’ll encounter.

(Here are the full 15 digits that the function uses, if you're wondering: 3.141592653589793. You have to stop somewhere, because pi goes on forever.)

The PI() function syntax

The syntax is super simple:

=PI()

There are no arguments or options to adjust. Actually, if you try to enter any arguments, Excel will return an error. So, always use empty parentheses.

Excel PI() in Well-Known Formulas

Now that you know what PI() is and how to use it, let’s see it in action. In this section, we’ll explore practical ways you can apply PI() in your daily Excel work, from calculating areas and circumferences to more advanced applications.

Calculating the area of a circle using PI()

Suppose you need to calculate the area of a circle from its radius. The formula you’d use by hand is Area = π × r^².

If your circle’s radius is in cell A2, enter this formula to calculate the area:

=PI() * (A2^2)

This multiplies pi by the radius squared, giving you the area in square units.

Finding the circumference of a circle

Similarly, the circumference of a circle is given by 2 × π × r. In Excel, you can write:

=2 * PI() * A2

Here, A2 is the radius. This formula gives the circle’s circumference.

Using PI() in trigonometric calculations

Sometimes, you’ll need to perform calculations involving angles, such as converting degrees to radians. Since Excel’s trigonometric functions like SIN() and COS() use radians, PI() helps bridge the gap.

To convert degrees to radians, you will take the degrees and multiply by pi and then divide by 180.

=A2 * PI() / 180

Notice that for 180 degrees, the value returns π, since 180 degrees equals π radians. In this case, the 180 cancels out.

Using PI() for the volume of a cylinder

Not surprisingly, pi shows up in scientific and engineering calculations. For example, to calculate the volume of a cylinder (π × r^² × h), you can use:

=PI() * (A2^2) * B2

Here, A2 is the radius and B2 is the height.

Using PI() to convert rotational speed

Pi plays a role in rotational motion, too. You could, for example, convert revolutions per minute (RPM) to angular velocity in radians per second. You could work it out because one revolution equals 2π radians. Depending on the context, you could also use π to relate RPM to linear speed by factoring in the radius of rotation. There are a lot of possibilities!

Tips, Tricks, and Common Mistakes

By now, you’ve seen the use of PI() in your Excel formulas. But, as with any Excel function, a few tips can save you from surprises down the line.

Avoid hardcoding the value of π

This one almost goes without saying, since it's a lot of the point of this article! It can be tempting to sometimes type “3.14” by hand. But this approach is error-prone and less precise. Sometimes, it makes a big difference.

Now, If you want fewer decimal places, just format the cell to display the right number, rather than shortening the formula’s output.

Remember: PI() takes no arguments

Don’t add anything inside the parentheses—Excel will throw a #VALUE! error if you do. The correct usage is always PI(), with nothing in between.

Leverage cell references for flexible formulas

If you’re calculating multiple areas or circumferences, use cell references to avoid retyping. For example, if you list radii in column A, you can drag your formula down column B to instantly calculate areas for each row. I've tried to keep my own advice in mind when sharing the screenshots so far.

Combining PI() with Other Excel functions

PI() plays well with almost every math or trigonometric function in Excel. It would have to because pi is only one part of many of the math formulas we know and use.

For example, here is the spherical law of cosines, which calculates the distance between two points on Earth. As you can see, in this formula, we use pi with a variety of trig functions, including COS(), SIN() and ACOS(). B2 and C2 refers to the latitude and longitude of Denver; B3 and C3 refer to the latitidue and longitude of Edinburgh.  

=3958*ACOS(SIN(B2*PI()/180)*SIN(B3*PI()/180)+COS(B2*PI()/180)*COS(B3*PI()/180)*COS((C3-C2)*PI()/180))

The distance is pretty similar as Google would have it (4,405 miles). 

This is one of those cases where the PI() function is absolutely needed because if you truncate the numbers you won't capture the curvature of the earth correctly and your distances will be off. To test that idea, I tried the formula again but shortened the value of pi, and got 4,418.3 miles, which was noticeably less accurate. So, don't use the PI() function and don't cut the numbers if you don't have to!

Conclusion

Don't stop here. Enroll in our Advanced Excel Functions course to master different mathematical, statistical, and logical functions in Excel. Each one is another step toward becoming an advanced Excel user, by which I mean becoming someone who can solve problems, automate processes, and find insights others might miss.