Pie Chart Calculator

What the pie chart calculator does

A pie chart shows how a whole splits into parts, with each slice sized by its share of the total. This calculator takes your values, works out what percentage of the total each one makes up and the angle of its slice, lays them out in a table, and draws the pie.

It is the classic way to show parts of a whole at a glance, from a budget broken into categories to a vote split between options. Below is how it works and when it is the right chart to reach for.

How to use it

1. Enter your values in the box, separated by commas, spaces, or new lines, one number per category.
2. Press Calculate for the percentage and angle of each slice, plus the pie chart, or Reset to clear it.

How the shares and angles are worked out

First the calculator adds all your values to get the total. Then, for each value, it works out two things. The percentage is that value's share of the total:

Percentage = (value ÷ total) × 100

The angle is how wide that slice opens, out of the full 360 degrees of the circle. Since the whole circle is the total, each slice takes the same share of the 360 degrees as it does of the data:

Angle = (percentage ÷ 100) × 360

The percentages add up to 100 and the angles add up to 360, which is what closes the circle. The angle is handy if you are ever drawing a pie chart by hand with a protractor.

When a pie chart is the right choice

Pie charts work best under a few conditions. The values should be parts of a single whole, so that adding them up and taking shares actually means something, a breakdown of one budget rather than unrelated figures. And there should be only a handful of slices, since a pie sliced into a dozen thin wedges is hard to read.

When the slices are many, or close in size, or you want to compare precise amounts, a bar chart usually does the job better, because lengths are easier for the eye to judge than angles. So reach for a pie when the story is one of proportion, a few clear parts making up a whole, and reach for a bar chart when the story is about comparison.

A worked example

Suppose four categories have the values 40, 25, 20, and 15, which add up to a total of 100.

Each value's percentage is its share of that 100, so the slices are 40 percent, 25 percent, 20 percent, and 15 percent. The angles are those shares of 360 degrees: 144, 90, 72, and 54 degrees. The percentages add to 100 and the angles add to 360, so the circle closes exactly.

Entering your data, and the labels

You can separate your numbers with commas, spaces, or new lines, in any mix. The calculator labels the slices Group A, Group B, and so on in the order you enter them, so make a note of which value is which as you type. Percentages and angles are shown to two decimal places. Pie charts assume positive values, since a slice is a share of a whole, so this works with counts and amounts rather than data that can go negative.

Questions people ask

What does a pie chart show?

How a whole divides into parts, with each slice sized by its share of the total. It is best for showing proportions at a glance.

How is the angle of a slice found?

By taking the slice's share of the total and applying it to the full 360 degrees of the circle. A slice that is a quarter of the data opens 90 degrees.

What do the slices add up to?

The percentages add to 100 and the angles add to 360. That is what makes the slices fill the whole circle exactly.

When should I use a bar chart instead?

When you have many categories, slices of similar size, or you want to compare precise amounts. Lengths are easier to judge than angles, so bar charts suit comparison better.

References

A quick note on where the methods here come from. Pie charts and other displays for categorical data are set out in the NIST/SEMATECH e-Handbook of Statistical Methods, the US government's public statistics reference. OpenStax Introductory Statistics is a free, widely used textbook that covers pie charts and when to use them.

1. NIST/SEMATECH e-Handbook of Statistical Methods (graphical techniques for data). https://www.itl.nist.gov/div898/handbook/
2. OpenStax, Introductory Statistics (displaying categorical data). https://openstax.org/details/books/introductory-statistics-2e