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RDMAICS • FREE PROCESS IMPROVEMENT TOOLS

Sample Size for a Proportion

Plan a random sample for a population proportion with an absolute margin of error.

Measure

Sample Size for a Proportion

Browser-only calculations · No input data saved

For tables: one row per line, comma-separated columns, no header row. Avoid commas inside labels. Changing an input clears previous results.

Worked example results

Z critical
1.959964
Uncorrected n
384.145883
Required sample (rounded up)
385

Rounded for display only. Export includes the inputs, results, method and assumptions. Refreshing or leaving the tool clears entered data.

How to use Sample Size for a Proportion

  1. Load the worked example to see the required input format.
  2. Plan a random sample for a population proportion with an absolute margin of error. Use consistent units, periods and definitions.
  3. Select Calculate, review the assumptions and export the result for your project evidence.

Formula and method

n₀ = z²p(1−p)/e². With population N: n = n₀ / (1 + (n₀−1)/N). Round up only after correction.

Interpretation and assumptions

Normal-approximation planning for simple random sampling, not acceptance sampling or power analysis. Use p=50% when unknown. Small expected success/failure counts need an exact method.

Results support professional judgement. They are not a certification of process stability, a financial commitment or a substitute for study design.

Keep the evidence connected

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Frequently asked questions

How do I use the sample size for a proportion?

Plan a random sample for a population proportion with an absolute margin of error. Load the example first, then replace all inputs with consistent process data and select Calculate. n₀ = z²p(1−p)/e². With population N: n = n₀ / (1 + (n₀−1)/N). Round up only after correction.

What assumptions matter for sample size for a proportion?

Normal-approximation planning for simple random sampling, not acceptance sampling or power analysis. Use p=50% when unknown. Small expected success/failure counts need an exact method.

Are my calculator inputs saved or sent to a server?

These native calculations run in this browser tab. Inputs are not sent to a server or saved by this calculator. Download the result if you need a record; leaving or refreshing clears the form.