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Sample Size Calculator

Use this free sample size calculator to estimate a survey sample size from confidence level, margin of error, estimated proportion, and optional population size.

All tools
Formula steps Examples included Copy results Private history
Required sample size385
Z-score
1.96
Raw n
384.16
Adjusted n
n/a

How to use the sample size calculator

  1. Choose a confidence level such as 90%, 95%, or 99%.
  2. Enter the margin of error and estimated population proportion as percentages.
  3. Add a finite population size only when you know the population is limited.
  4. Press Calculate sample size to see the required sample and formula steps.

Common uses

Estimate how many survey responses you need for a proportion.

Compare 90%, 95%, 98%, and 99% confidence levels.

Use 50% estimated proportion for a conservative planning estimate.

Apply finite population correction when the total population is known.

Examples

Common survey 95%, 5% margin, 50% proportion

385

Finite population 95%, 5%, 50%, population 1,000

278

Higher confidence 99%, 5%, 50%

664

Frequently asked questions

Quick answers about formulas, inputs, examples, result copying, and private in-browser history.

What kind of sample size does this calculator estimate?

It estimates sample size for a population proportion, which is common for surveys, polls, yes/no questions, and percentage estimates.

What should I enter for population proportion?

Use your best estimate. If you are unsure, use 50%, which gives the most conservative and usually largest sample size.

What is margin of error?

Margin of error is the maximum difference you are planning to tolerate between the sample estimate and the true population proportion.

What does finite population correction do?

When the total population is known, finite population correction can reduce the required sample size because the sample is a larger share of the whole group.

Can this replace professional survey design?

No. It is a planning calculator for common proportion estimates. Professional surveys may need design effects, stratification, weighting, and nonresponse planning.

Is my sample size history private?

Yes. Recent sample size answers stay only in the current browser tab while you use the page. They are not sent to a server.

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