Pie Chart Calculator
Enter your category values below and this calculator instantly converts them into the percentage share and central angle for every slice of the pie. You can name each category yourself or leave the default labels. The results update as you type and include a full breakdown table, a donut chart, and a step-by-step worked solution showing exactly how each figure was reached.
Formula
Worked example
Suppose a company budget has four departments: Sales 40, Marketing 30, Operations 20, Other 10. Total = 100. Sales percentage = 40/100 x 100 = 40%, angle = 40/100 x 360 = 144 degrees. Marketing = 30%, 108 degrees. Operations = 20%, 72 degrees. Other = 10%, 36 degrees. All percentages sum to 100 and all angles sum to 360.
What is a pie chart?
A pie chart is a circular diagram divided into slices, where each slice represents a category and its size is proportional to the category's share of the total. The whole circle represents 100% or 360 degrees. Pie charts are best used when you want to show how a single quantity is divided among a small number of discrete parts, and when the relationship between parts and the whole is more important than differences between the parts themselves.
How to calculate pie chart percentages and angles
There are two quantities to find for each slice. First, the percentage: divide the slice value by the total of all values, then multiply by 100. Second, the central angle: divide the slice value by the total, then multiply by 360. Both calculations start from the same ratio, so a quick shortcut is to find the percentage first and then multiply it by 3.6 to get the degrees. For example, a category that represents 25% of the total occupies 25 x 3.6 = 90 degrees, which is one quarter of the full circle. The calculator on this page works out both figures for every category simultaneously.
When to use a pie chart and when to avoid it
Pie charts communicate part-to-whole relationships clearly when there are no more than five or six slices, the differences between slices are large enough to be visible, and you are not asking the reader to make precise numerical comparisons. They become harder to read when slices are similar in size, when more than six or seven categories are needed, or when you need to compare totals across multiple datasets (a bar chart or stacked bar chart is better for that). Very small slices, say below 3 to 5 percent, are almost impossible to distinguish by angle alone and are usually better grouped into an "Other" category.
Pie charts vs donut charts and other alternatives
A donut chart is identical to a pie chart in its mathematics; it simply has a hollow center that can be used to display a total or a key figure. Research suggests the two formats are roughly equally readable for most audiences. If you need to compare two pie charts side by side, a grouped or stacked bar chart almost always communicates the comparison more accurately, because human perception of linear length is more precise than perception of area or angle. Waffle charts and treemaps are other alternatives for part-to-whole data that trade the circular form for a grid or nested rectangle layout.
Pie chart angle reference
| Percentage | Central angle | Fraction of circle |
|---|---|---|
| 5% | 18° | 1/20 |
| 10% | 36° | 1/10 |
| 12.5% | 45° | 1/8 |
| 16.7% | 60° | 1/6 |
| 20% | 72° | 1/5 |
| 25% | 90° | 1/4 |
| 33.3% | 120° | 1/3 |
| 50% | 180° | 1/2 |
| 66.7% | 240° | 2/3 |
| 75% | 270° | 3/4 |
| 100% | 360° | Full circle |
Quick reference for common percentage-to-angle conversions. Multiply any percentage by 3.6 to get the central angle.
Frequently asked questions
How do I calculate the angle for a pie chart slice?
Divide the slice value by the total of all values, then multiply the result by 360. For example, if one category has a value of 25 and the total is 100, the angle is (25 / 100) x 360 = 90 degrees. Equivalently, calculate the percentage first (25%) and then multiply by 3.6 to get 90 degrees.
How do I find the percentage for each pie chart slice?
Divide the value of the slice by the sum of all values and multiply by 100. The formula is: percentage = (slice value / total) x 100. Enter your values above and this calculator performs all the divisions automatically.
Why must all pie chart angles add up to 360 degrees?
A circle contains exactly 360 degrees. Because each slice angle is proportional to that category's share of the whole, and because all the shares together equal 100% of the data, the angles must also sum to 100% of the circle, which is 360 degrees. If your hand-calculated angles do not sum to exactly 360, it is usually due to rounding each angle individually. Rounding errors accumulate; they are typically less than 1 degree and are a normal artifact of the arithmetic.
Can I use non-integer values?
Yes. The formulas work with any positive numbers, including decimals. The calculator accepts decimal values and shows results to two decimal places. The only requirement is that every value must be zero or positive, and at least one value must be greater than zero.
How many slices should a pie chart have?
Most data visualization guidelines recommend a maximum of five to seven slices. Beyond that, the smallest slices become too thin to label clearly and the chart becomes difficult to interpret. If you have more categories, group the smaller ones into an "Other" or "Remaining" category so the chart stays readable.
What is the difference between a pie chart and a donut chart?
A donut chart is simply a pie chart with the center cut out. The mathematics are identical: the same percentage and angle formulas apply. The hollow center of a donut chart can display a total, a label, or another data point. Neither format is decisively better; choose whichever looks clearer in your specific context.