# Sample Size Calculator

> Calculate a required survey sample size or the margin of error for a proportion, including finite-population correction.

Page: https://askcalculators.com/calculator/sample-size-calculator/
Definition: https://askcalculators.com/calculator/sample-size-calculator/definition.json
JSON Schema: https://askcalculators.com/calculator/sample-size-calculator/schema.json
Version: 2.0.0
Maintained by: AskCalculators (software project; not a credentialed reviewer)
Qualified review: pending. Automated checks do not establish professional approval.
Page status: Live
Review status: Pending

## Use
Open the calculator page and enter values. Query-string parameters can restore and bookmark a calculation.
Example: https://askcalculators.com/calculator/sample-size-calculator/?calculation=sample-size&confidenceLevel=95&populationProportion=50&marginOfError=5

## Inputs
- calculation: Calculate; type=select; required; default=sample-size; values=sample-size|margin-error
- confidenceLevel: Confidence level; type=select; required; default=95; values=80|85|90|92|95|96|98|99|99.9
- populationProportion: Population proportion; type=percent; required; default=50; min=0.0001; max=99.9999
- populationSize: Population size (optional); type=number; optional; min=1
- marginOfError: Desired margin of error; type=percent; required; default=5; min=0.0001; max=99.9999; showWhen=calculation:sample-size
- sampleSize: Observed sample size; type=number; required; default=385; min=1; showWhen=calculation:margin-error

## Outputs
- requiredSampleSize: Required sample size; format=integer; primary
- marginOfErrorResult: Margin of error; format=percent
- confidenceInterval: Confidence interval; format=text
- criticalZ: Critical z-score; format=number
- finiteCorrection: Finite-population correction; format=number

## Formula
n₀=z²p(1−p)/e²; finite n=n₀/[1+(n₀−1)/N]; e=z√[p(1−p)/n] with finite correction.

## Rules
- Empty optional inputs are undefined, not zero.
- Hidden conditional inputs are ignored.
- Do not invent missing required inputs.