How To Work Out The Percentages For A Pie Chart

A pie chart displays a set of categories' proportions, or percentages of the total, in a visual way. To accurately create a pie chart, you must first work out the percentage of the pie chart that each category should occupy. From there, you can calculate the angle that each piece of the pie should have.

1. Categorize Your Data

Compile your data into categories. Assign each category a number. For example, if you have statistics on four categories of university majors, you might wish to turn that data into a pie chart. You might find the following: there are 410 art majors, 420 science majors, 900 language majors, and 540 engineering majors.

2. Find the Total

Add all the numbers together to get the total. In this case:

\(410 + 420 + 900 + 540 = 2270\)

3. Divide the Categories

Divide each of the categories by the total. You results will be a list of decimals under 0. Round, if necessary. In the example, with rounding:

\(\text{Art: } 410 ÷ 2270 = 0.18\)
\(\text{Science: } 420 ÷ 2270 = 0.18\)
\(\text{Language: } 900 ÷ 2270 = 0.40\)
\(\text{Engineering: } 540 ÷ 2270 = 0.24\)

4. Convert to Percentages

Multiply each of the decimals by 100 to get the percentages. You can easily do this by moving the decimal point two places to the right. In the example:

Art: 18 percent

Science: 18 percent

Language: 40 percent

Engineering: 24 percent.

These percentages will be the labels for each section.

5. Calculate the Degrees

Multiply the decimals from Step 3 by 360 to get the number of degrees each slice of pie should take up in the pie chart. For the example, this yields the angles 64.8, 64.8, 144 and 86.4 for the categories of art, science, language and engineering, respectively.