Pie Chart Calculator
A slice of a pie chart is a share of 360 degrees. In a 2,900 dollar budget, rent of 1,450 takes 180 degrees, exactly 50 percent of the circle, and food at 520 takes 64.6 degrees. Six slices are enough for most charts.
Enter up to six slices from one whole, such as budget lines or survey answers. The calculator returns the percent share and the central angle of every slice, draws the chart, and checks that the angles close the circle at 360 degrees.
| Total of all slices | |
| Largest slice | |
| Slices drawn | |
| Angle check | |
Each percent is value divided by total times 100, and each central angle is that percent times 3.6 degrees. A pie chart only makes sense when the values are parts of one whole, so do not mix units or add negative numbers. All calculations run in your browser, and nothing you type is uploaded or stored.
Turn a list of values into pie slices: each share as a percent, each slice as a central angle in degrees, and a drawn chart you can check at a glance.
Key takeaways
- One percent of a pie is 3.6 degrees, so a 25 percent slice spans 90 degrees
- Angle = value / total x 360, and the percent share is the same ratio x 100
- In the budget example, rent of 1,450 out of 2,900 takes half the circle at 180 degrees
- Keep a chart to about 6 slices and fold the tail into one Other slice
- About 1 in 12 men has a color vision deficiency, so label slices with names, not color alone
On this page
- Angles, not areas: what a pie chart shows
- The two formulas: share and central angle
- Worked example: a 2,900 dollar monthly budget
- Worked example: reading a slice backwards
- How many slices are too many
- Order, grouping and the Other slice
- Color, contrast and color blindness
- When a pie chart is the wrong tool
Angles, not areas: what a pie chart shows
A pie chart is a circle cut into wedges, and the size of each wedge is set by the central angle at the middle of the circle. A full circle is 360 degrees, so a slice holding 1 percent of the total spans 3.6 degrees. Half of the data fills 180 degrees, a quarter fills 90 degrees, and a tenth fills 36 degrees.
That is the whole idea, and it is worth stating plainly, because a pie chart only works when the values are parts of one whole. Every slice has to be measured in the same unit, and the numbers have to add up to something meaningful: dollars in a budget, votes in an election, respondents in a survey. Mixing a monthly rent with a yearly total puts a slice in the chart that means nothing.
People argue about pie charts because the eye compares angles and areas badly. A slice covering half the circle is easy to see, but two slices at 18 percent and 22 percent look nearly the same even though one is a quarter bigger. That is a reading problem, not a math problem.
The two formulas: share and central angle
Every pie chart is built from two lines of arithmetic. First the share: percent = value / total x 100. Then the angle: degrees = value / total x 360. The second line is the first line multiplied by 3.6, because 360 divided by 100 gives 3.6 degrees for each percent.
| Share of the total | Central angle | How the wedge looks |
|---|---|---|
| 1 percent | 3.6 degrees | a hairline sliver |
| 5 percent | 18 degrees | a thin slice |
| 10 percent | 36 degrees | about a tenth of the circle |
| 25 percent | 90 degrees | exactly one quarter |
| 33.3 percent | 120 degrees | one third |
| 50 percent | 180 degrees | half the circle |
| 75 percent | 270 degrees | three quarters |
The angle formula is the one to remember when you are building a chart by hand in a spreadsheet or a graphics program. Type the percentage, multiply by 3.6, and the slice angle drops straight into the program. Most drawing tools also accept a percentage directly, which saves the step entirely.
One caution about rounding. Percentages rounded to one decimal place can add up to 99.9 or 100.1 percent, and angles rounded the same way can miss 360 by a few tenths of a degree. That is normal. Check the total, mention the rounding in the caption, and do not fudge one slice to force the sum to land on exactly 100.
Worked example: a 2,900 dollar monthly budget
Take a monthly budget that adds up to 2,900 dollars: rent 1,450, food 520, transport 310, utilities 210, savings 260, and other 150. The rent line is 1450 / 2900 x 100, which is 50.0 percent, and 50 percent of 360 degrees is 180 degrees. Rent takes exactly half the circle and starts at 12 o'clock.
| Slice | Value | Percent share | Central angle |
|---|---|---|---|
| Rent | 1,450 | 50.0 percent | 180.0 degrees |
| Food | 520 | 17.9 percent | 64.6 degrees |
| Savings | 260 | 9.0 percent | 32.3 degrees |
| Transport | 310 | 10.7 percent | 38.5 degrees |
| Utilities | 210 | 7.2 percent | 26.1 degrees |
| Other | 150 | 5.2 percent | 18.6 degrees |
| Total | 2,900 | 100.0 percent | 360.0 degrees |
Food is the interesting one because it does not land on a round number. 520 / 2900 x 100 is 17.931 percent, and the angle is 17.931 x 3.6, which is 64.55 degrees. Transport comes out at 38.48 degrees and utilities at 26.07 degrees. Add the six angles back together and they close the circle at 360.0 degrees, which is the check the calculator runs on every set of numbers you enter.
Notice that savings, at 260 dollars, is bigger than utilities at 210 dollars and gets a wider wedge. Sorting by size makes that easier to see, and it is the order the calculator uses by default.
Worked example: reading a slice backwards
Sometimes you are the reader rather than the chart maker. A slice marked with a 45 degree angle tells you its share straight off, because 45 / 360 is 0.125, so the slice holds 12.5 percent of the whole. In the 2,900 dollar budget above, that slice is worth 2900 x 0.125, which is 362.50 dollars.
The same trick works on any chart. Find the angle, divide it by 360 to get the fraction, then multiply by the total printed in the middle of the pie. If the chart prints percentages instead of angles, the route is one step longer: multiply the percentage by 3.6 to get the angle, then divide by 360.
This is also how you check a chart that looks wrong. If a slice claims 30 percent but its wedge looks like a fifth of the circle, the wedge is telling you that the label is wrong or that the chart was not drawn to scale. Charts do carry errors like this, so the arithmetic is worth doing before you repeat a number to somebody else.
How many slices are too many
Most people who dislike pie charts dislike the eight slice version with a legend the width of a phone screen. The Census Bureau put it plainly in a 2017 technical note on data visualization: the human mind reads circular area and angles poorly, so pie charts can mislead with more than two or three slices.
Two or three slices is comfortable. Four to six is workable if every slice carries a label and the smallest ones are not hairlines. Past that, the angles get hard to compare and the chart turns into a legend with a picture next to it. A horizontal bar chart of the same six values is easier to read, because bar lengths share a common baseline and the eye compares them without effort.
| Number of slices | What happens | What to do |
|---|---|---|
| 2 or 3 | clean, easy to compare | keep the pie |
| 4 to 6 | workable with direct labels | keep it and label every slice |
| 7 or more | hard to read, angles get thin | group the tail or switch to a bar chart |
The same note also warns against three dimensional pie charts, which is good advice. A raised slice takes up more room on the page than a flat one, so the reader ends up judging an area that no longer matches the data. Flat wedges with a thin white border between them look cleaner and mislead less.
Order, grouping and the Other slice
Order the slices from largest to smallest, then start at 12 o'clock and run clockwise. Readers scan a pie like a clock, and the biggest slice in the usual position gives the eye something solid to land on.
When the tail is long, group it. If five slices are each under 5 percent, fold them into one slice called Other and print the detail in a note under the chart. The information is not lost, and the chart gets a readable shape. The trade is honest as long as the caption says how many categories are hidden inside the Other slice.
A real example of a pie chart doing its job is the US electricity mix. The Energy Information Administration reported that in 2023 natural gas produced 43.1 percent of utility scale electricity, nuclear 18.6 percent, coal 16.2 percent, renewables 21.4 percent, and petroleum and other sources the remaining 0.8 percent. On a pie the gas slice alone spans 155.2 degrees, since 43.1 x 3.6 is 155.16, and renewables at 21.4 percent span 77.0 degrees. Five slices, one of them dominant, and the shape of the chart tells the story before a single label is read.
Color, contrast and color blindness
Color in a pie chart does real work when the slices are far apart in size, and it gets in the way when they are not. The practical advice from federal accessibility guidance is simple: never let color be the only thing carrying the meaning. About 1 in 12 men and about 1 in 200 women experience color blindness, according to the National Eye Institute, cited by the Section 508 program, and a red and green pair that looks obvious to you can look like one color to them.
Two rules handle this. Label every slice directly with its name and value, and use color as reinforcement rather than as the carrier of the information. And keep contrast high enough that the wedges separate from the background and from each other. WCAG 2.1 success criterion 1.4.11 asks for a contrast ratio of at least 3 to 1 for the parts of a graphic needed to understand the content.
Color choices that survive most forms of color blindness, such as blue next to orange or dark gray next to light gray, also happen to print better in a report. If the chart will be printed in black and white, test it that way, because if two slices become the same shade the chart has already lost a reader before anyone with a color vision deficiency sees it.
When a pie chart is the wrong tool
Some questions a pie chart cannot answer well. Change over time belongs in a line chart. Comparing two groups belongs in a grouped bar chart, because two pies side by side force the reader to compare angles across two separate circles. Values that are not parts of a whole, such as a company's revenue and its profit in the same year, do not belong in a pie at all, because there is no meaningful whole to divide up.
| Question | Best chart | Why |
|---|---|---|
| How did spending change over 12 months? | line chart | time runs along one axis |
| Which of two groups spent more? | grouped bar chart | bars share a baseline |
| What share of the budget is rent? | pie chart | rent is a part of one whole |
| How do 40 items rank? | bar chart | angles are too fine to rank |
The comparison inside this calculator is worth making too. The chart on screen shows the shape of the data, and the table under it gives the exact numbers you need for a report. Government charts often carry both.
Everything on this page runs in your browser and nothing you type is uploaded or stored. The sources behind the page are the Census Bureau technical note on data visualization from 2017, the EIA FAQ on US electricity generation by source, using 2023 data, the Section 508 guide to accessible color use, and the WCAG 2.1 guide to non-text contrast.
Frequently asked questions
How do I turn a number into a pie slice?
Divide the value by the total and multiply by 360 to get the degrees, or by 100 to get the percent. A slice worth 50 out of 200 spans 90 degrees and takes 25 percent of the pie.
What percent of a pie is a 90 degree slice?
A 90 degree slice is a quarter of the circle, so 25 percent. The rule is percent = degrees / 3.6, since 360 degrees spread over 100 percent gives 3.6 degrees for each percent.
How many degrees is 1 percent of a pie?
3.6 degrees, because a full circle of 360 degrees holds 100 percent. A 10 percent slice spans 36 degrees and a 50 percent slice spans 180 degrees.
How many slices should a pie chart have?
Two or three is comfortable, and four to six still work with direct labels. The Census Bureau (2017) notes that pie charts can mislead, especially with more than two or three slices, so group the tail or use a bar chart.
Do the percentages have to add up to exactly 100?
They do in the raw data, but rounding to one decimal place can leave a sum of 99.9 or 100.1 percent. Check the total and note the rounding instead of forcing one slice to make the sum land on 100.
Can a pie chart show negative numbers?
No. A negative value has no wedge. Pull anything below zero out of the data first, for example by netting a refund against the category it belongs to, then build the chart from the net figures.
Why do people say pie charts are bad?
Because the eye compares angles and areas poorly, and the Census Bureau (2017) says pie charts can mislead with more than two or three slices. They work well for one clean part to whole split with a few labeled slices.
Should I sort the slices?
Yes, largest first, starting at 12 o'clock and running clockwise. In the budget example that puts rent at 1,450 dollars and 180 degrees first, and it puts the smallest slices last where they are easiest to skip.
What is the best way to label slices?
Put the name and the value directly on or next to each wedge, and keep a legend as a backup. Do not rely on color alone, since about 1 in 12 men has a color vision deficiency according to the National Eye Institute.
Can I use a donut chart instead?
Yes. A donut chart uses the same angles and the same math, with a hole in the middle. The hole is useful for a total in the center, but it takes away some of the angle signal, so label the slices as carefully as you would on a pie.
How do I read a value from a chart with no percentages?
Find the angle, divide it by 360 to get the fraction, then multiply by the total. A 45 degree slice of a 2,900 dollar total is 0.125 x 2900, which is 362.50 dollars.
How do I make a pie chart in a spreadsheet?
Enter the label and value in two columns, then pick a pie chart from the insert menu. Most spreadsheet charts take raw values or percentages and do the angle math for you, which is the same 3.6 degrees for each percent rule.
What is the Other slice for?
It collects the small categories so the chart stays readable. If five slices each sit under 5 percent, group them, and say in the caption how many categories are hidden inside the Other slice.
Does the order of slices change what the chart means?
No, as long as the angles match the values. Order changes how fast a reader finds a slice, not what the chart says. Start at 12 o'clock and run clockwise, which is the order most readers expect.
Should the percentages be printed on the chart?
Print the percent when the audience needs the share, and the raw value when the audience needs the dollars. A household budget chart is more useful with both, for example rent at 1,450 dollars and 50.0 percent.
Spotted a wrong number or a broken result?
More Math tools
Fee schedules, rates and rules change without notice. Always confirm important figures with the official source before you rely on them.