How this instrument works
A pie chart's slices are proportional to each category's share of the grand total, and the most common way to express that share is as a percentage — value divided by total, scaled to a base of 100. A category worth 13 out of 50 total is 26% of the pie: (13/50) × 100 = 26. This is the figure that typically appears in a data table, a legend, or a hover-label next to each slice, since percentages are more immediately readable than raw counts when comparing categories of very different sizes.
The same underlying ratio also determines the slice's physical angle in the finished chart (percentage times 3.6 gives degrees, since 360/100 = 3.6), but the percentage itself is usually the number analysts compute and report first — it's unit-independent and easy to compare across different datasets, unlike raw counts, which only make sense relative to their own total.
Every category's percentage in a properly constructed pie chart sums to 100% across the whole chart — if your percentages don't add up to 100, allowing for rounding, the most likely cause is that total wasn't actually the sum of every category, or that a category was double-counted or left out somewhere in the underlying data.
- Enter the slice's value into Slice value — the raw amount this one category represents.
- Enter the sum of every slice into Total — all categories combined, including this one.
- Read Slice percentage — this slice's share of the whole, out of 100.
- Repeat for every category; the percentages should sum to 100% across the full chart.
Worked example — 13 of 50 total responses
A survey category received 13 responses out of 50 total responses across every category. Enter 13 into Slice value and 50 into Total.
Percentage = (13/50) × 100 = 26% exactly. That's the figure you'd put directly into a data table or a chart legend next to this category's slice — no further conversion needed unless you're also drawing the physical wedge, in which case you'd additionally need the angle in degrees.
Questions
How do I turn this percentage into a slice angle for drawing the chart?
Multiply the percentage by 3.6, since a full circle is 360 degrees and 360 divided by 100 is 3.6 — so a 26% slice becomes a 93.6-degree wedge. This site's dedicated pie-chart-angle calculator does that conversion directly from the same value-and-total inputs, or the combined pie-chart calculator returns both the percentage and the angle together.
Why don't my percentages add up to exactly 100%?
The most common cause is rounding — if each category's percentage is rounded to a whole number or a couple of decimal places before summing, small rounding errors can push the total slightly above or below 100%. The other common cause is that total wasn't actually the sum of every category's value; double-check that no category was accidentally left out of, or double-counted in, the total used.
Can the percentage be negative?
No — a slice value should always be zero or positive, and the total should always be positive and at least as large as any single slice, so the resulting percentage will always fall between 0% and 100%. If your data legitimately includes negative values, a standard pie chart isn't really the right way to visualize it, since pie charts assume every category is a non-negative share of one meaningful whole.
What's the difference between this and just computing value/total myself?
Nothing mathematically — this calculator is exactly that division, multiplied by 100, with the arithmetic done for you and the result rounded cleanly. Its main value is convenience and avoiding a manual slip when computing percentages for several categories in a row, especially when the total itself is an awkward number to divide by mentally.