Circle Graph Calculator: Make a Pie Chart

This circle graph calculator turns your list of values into the angles and percentages you need to draw a pie chart. You enter the raw numbers (or percentages) for each category, and it returns each slice’s central angle in degrees and its share of the whole as a percent. The result is exactly what you’d plot with a protractor or feed into charting software.

Formula

The circle (or pie) graph is a simple proportional representation. For each category i with value v_i, the total is T = v₁ + v₂ + … + v_n. Then:

• Angle = (v_i / T) × 360°
• Percentage = (v_i / T) × 100%

All angles are measured in degrees, and the sum of all angles always equals 360° (or very close, after rounding). The sum of all percentages equals 100%.

Worked Example

Using the default values from the calculator: Category A = 50, Category B = 30, Category C = 20.

1. Total T = 50 + 30 + 20 = 100.
2. Angle A = (50 / 100) × 360 = 0.5 × 360 = 180.0°
3. Angle B = (30 / 100) × 360 = 0.3 × 360 = 108.0°
4. Angle C = (20 / 100) × 360 = 0.2 × 360 = 72.0°
5. Check: 180 + 108 + 72 = 360°.
6. Percent A = (50 / 100) × 100 = 50.0%

These match the calculator’s output exactly.

When to Use a Circle Graph

A pie chart is best when you want to show how a whole is divided into parts—market share, budget allocation, survey responses, or time spent on activities. Use it when you have a small number of categories (typically 2–7) and the parts add up to a meaningful total. If you have many categories or the values are very close, a bar chart is often clearer. Also, avoid using pie charts for data over time; a line chart is better for trends.

How to Read the Results

The angle tells you exactly how wide each slice should be when you draw the circle. The percentage tells you the proportion, which is often what people quote in reports. For example, a slice with 25% of the total corresponds to a 90° angle (a quarter of the circle). If you’re using software like Excel or Google Sheets, you usually don’t need the angle—just enter the raw values and the program draws the chart. But if you’re making a physical drawing or a custom graphic, the angle is essential.

Common Mistakes and Pitfalls

• Using percentages that don’t sum to 100: If you enter percentages directly, make sure they add up to 100. Otherwise the calculator will treat them as raw numbers and the result will be off.
• Rounding too early: If you round each angle to the nearest degree before summing, you might get 359° or 361°. That’s normal—just adjust one slice by a degree.
• Confusing degrees with radians: This calculator outputs degrees. If you’re using a programming language that expects radians, convert by multiplying by Ï€/180.
• Zero or negative values: A zero value produces a zero angle (no slice). Negative values don’t make sense in a pie chart; if you have them, you should re-examine your data.

Limits of the Formula

The formula is purely arithmetic—it assumes every category is mutually exclusive and the whole is exactly the sum of the parts. It does not account for uncertainty, missing data, or categories that overlap. It also doesn’t tell you whether a pie chart is the right visual choice; that’s a judgment call. For large numbers of categories, the slices become too thin to label legibly, so consider grouping small categories into an “Other� slice.

Frequently Asked Questions

Can I enter percentages instead of raw numbers?

Yes, as long as they sum to 100. The calculator treats any numbers as weights; if your percentages sum to 100, the angles and percentages will be correct. If they sum to something else, the result will reflect that total, not 100%.

What if my categories have very different magnitudes?

That’s fine. The formula scales automatically. For example, if one category is 1,000 and another is 10, the first will get a much larger slice. Just be aware that tiny slices may be hard to see or label.

How do I draw the circle graph by hand?

Draw a circle, mark the center, and draw a radius from the center to the top (12 o’clock position). Use a protractor to measure the first angle from that radius, draw the next radius, and continue. The angles from the calculator give you the exact slice boundaries.

Why do my angles not add up to 360 after rounding?

Because each angle is rounded to one decimal place, the sum may be 359.9° or 360.1°. That’s acceptable. If you need exact 360°, adjust the largest slice by the difference.

Can this calculator handle more than three categories?

This version has three inputs, but the formula is the same for any number. You can combine categories or use a spreadsheet for larger sets. The math doesn’t change.

Is a pie chart always the best choice?

No. Pie charts are best for showing parts of a whole with few categories. If you’re comparing values across categories (not parts of a whole), a bar chart is usually easier to read. Also, if you have more than 7 slices, consider a bar chart or a stacked bar.

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in a | Category A | - | 50 | 0
in b | Category B | - | 30 | 0
in c | Category C | - | 20 | 0
out angle_a | Angle A | degrees | a / (a + b + c) * 360 | 1
out angle_b | Angle B | degrees | b / (a + b + c) * 360 | 1
out angle_c | Angle C | degrees | c / (a + b + c) * 360 | 1
out pct_a | Percent A | % | a / (a + b + c) * 100 | 1