Pie Charts — Fundamental Concepts

Fundamental Concepts

Conversion triangle

Share = category amount / total. Percentage = share × 100. Sector angle = share × 360 degrees. Therefore amount = total × angle/360 or total × percentage/100.

Comparing pies

Use each chart's own total.
Convert shares to amounts before comparing absolute quantities.
A smaller share can represent a larger amount if the whole grows.
Percentage-point change is subtraction of percentages.
Relative percentage change divides that subtraction by the initial percentage.
Combined shares require weighting by totals.

Original comparison anchor

Health at 25 percent of ₹800 lakh is ₹200 lakh. At 20 percent of ₹1,200 lakh it is ₹240 lakh. Share: down 5 percentage points. Amount: up ₹40 lakh, or 20 percent. These are compatible findings, not a contradiction.

Validity checks

Categories should partition the named whole without double counting. Confirm whether the total means population, spending, output or another measure. Do not mix allocations with expenditure or different time periods without an explicit reason.

Missing information

Percentages alone establish composition and within-pie ratios. They do not establish amounts without a total. An “other” slice does not reveal its internal categories. Labels are more reliable than apparent area in a tilted or decorative chart. Always state whether the result describes a share, an amount, a percentage-point change or a relative percentage change.