Estimate a statistical sample size for a accessibility compliance audit using the population, desired confidence, margin of error, and expected exception rate. The calculation includes a finite-population correction, so smaller universes do not inherit an unnecessarily large infinite-population sample. This tool supports planning only: the sampling frame, random selection method, control objectives, and treatment of discovered exceptions still require professional judgment.
n₀ = z²p(1−p) ÷ e²; n = ceil[n₀ ÷ (1 + (n₀−1) ÷ N)]
The second expression applies the finite-population correction. The result is capped at the population size.
The result is the minimum rounded-up sample implied by the entered statistical assumptions, assuming a random and representative selection.
This planning estimate is not legal advice; confirm obligations, limitation periods, and enforcement rules with qualified counsel and the relevant authority.
For 1,000 items, 95% confidence, a 5% margin, and a 10% expected exception rate, the finite-population calculation rounds up to 122 sampled items.
No. It is a planning calculation based only on the values entered and does not determine legal obligations or outcomes.
Use controlling policy or legal values for requirements and measured operating data for time, cost, probability, or workload assumptions.
Run separate low, expected, and high scenarios and document the source and date of every assumption.
No. Compliance also depends on scope, controls, evidence, implementation quality, and the applicable jurisdiction or contract.
Recalculate after a rule, policy, contract, workload, staffing level, cost, control, or risk assumption changes.
| Variable | Meaning |
|---|---|
| N | Total eligible population |
| p | Expected exception proportion |
| e | Absolute margin of error |