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Percentage Sample Size Planner

Estimate how many responses you need for a percentage with a chosen margin.

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PDF report included

Responses needed

370

370 completed responses target a ±5 point margin at 95% confidence.

Large-group sample: 385
Expected answer: 50%
Confidence: 95%

Transparent breakdown

Target margin: 5%
Known population: 10,000
Completed responses: 370

Sample-size plan
Planning input	Value
Confidence	95%
Margin	±5 points
Expected share	50%
Responses needed	370

Use the result well

A clear answer, with the assumptions visible

These recommendations turn the result into an operational next step without hiding the inputs behind a score.

1
Invite extra people to cover non-response.
2
Use 50% when the expected answer share is unknown.
3
Choose respondents from the full group, not one easy segment.

How this tool works

Use jStat’s normal critical value for the selected confidence.
Calculate the large-group sample from expected share and margin.
Reduce it with a finite-population correction when a group size is known.

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