How to calculate a pie chart percentage
A pie chart divides a full circle among categories so each slice's size is proportional to its share of the total. To find any slice's percentage, divide that category's value (the "part") by the sum of all categories (the "total") and multiply by 100:
Percentage = (part / total) × 100
Because a whole circle is 360°, each slice's angle is proportional to the same fraction. You can get the angle either by multiplying the percentage by 3.6, or directly from the raw values:
Slice angle = (part / total) × 360 = percentage × 3.6
For example, if a category has a value of 40 out of a total of 200, its share is 40 / 200 = 0.20, which is 20% of the whole and a slice of 0.20 × 360 = 72°. Across every category the percentages must sum to 100% and the angles must sum to 360°.
Why the calculation is needed
Raw counts are hard to compare when totals differ. Converting each value to a percentage of the whole puts every category on a common 0–100 scale, which is what makes a pie chart readable. The angle conversion is the extra step you need if you are drawing the chart by hand or with a protractor, or verifying that a charting tool rendered slices at the correct size.
Common reference points
- 1% of the whole = 3.6° of the circle.
- 10% = 36°; 25% = 90° (a quarter, a right angle); 50% = 180° (a half); 75% = 270°.
- A slice that fills the whole pie is 100% = 360°; an empty category is 0% = 0°.
Sanity checks
The percentage can never exceed 100% unless the part is larger than the total, which usually signals a data-entry mistake. If you total the percentages of every slice and do not land on 100% (allowing for tiny rounding), one of the parts or the total is wrong.
Frequently Asked Questions
How do you calculate a pie chart percentage?
How do you convert a percentage into a slice angle?
Why don't my slice percentages add up to exactly 100%?
Can a pie chart percentage be more than 100%?
Common Tip Percentages
| Service | Typical Tip Range | Notes |
|---|---|---|
| Restaurant (sit-down) | 15–20% | 20%+ for exceptional service |
| Food delivery | 10–20% | Consider extra for long distances |
| Taxi / rideshare | 10–20% | More for assistance with luggage |
| Hotel housekeeping | $2–5/night | Leave daily, not just at checkout |
| Barber / hair salon | 15–20% | On pre-discount total |
| Pizza delivery | 10–15% or $3–5 minimum | Higher in bad weather |
General Household Budget Ratios (50/30/20 Rule)
| Category | % of Net Income | Examples |
|---|---|---|
| Needs | 50% | Rent, groceries, utilities, insurance |
| Wants | 30% | Dining out, entertainment, hobbies |
| Savings / Debt | 20% | Emergency fund, retirement, extra payments |
Common Measurement Conversions for Everyday Use
| Quantity | US / Imperial | Metric Equivalent |
|---|---|---|
| 1 cup | 8 fl oz | 237 mL |
| 1 pint | 16 fl oz | 473 mL |
| 1 quart | 32 fl oz | 946 mL |
| 1 gallon | 128 fl oz | 3.785 L |
| 1 lb | 16 oz | 453.6 g |
| 1 ft | 12 in | 30.48 cm |