Common survey
95%, 5% margin, 50% proportion385
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.
Inputs to checkExample numbersCopyable answerTab-only history
Required sample size385
- Z-score
- 1.96
- Raw n
- 384.16
- Adjusted n
- n/a
Recent answers
Recent answers will appear here.
Input tips
Use 50% proportion when you are unsure; it gives the most conservative survey sample size.
Optional population size applies finite population correction.
How to use the Sample Size Calculator
- Choose a confidence level such as 90%, 95%, or 99%.
- Enter the margin of error and estimated population proportion as percentages.
- Add a finite population size only when you know the population is limited.
- Press Calculate sample size to see the required sample and formula steps.
What people use it for
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.
See how a wider margin of error lowers the required response count.
Plan rough response targets before accounting for nonresponse or screening.
Quick examples
Finite population
95%, 5%, 50%, population 1,000278
Higher confidence
99%, 5%, 50%664
Wider margin
95%, 10%, 50%97
Estimated 20% yes rate
95%, 5%, 20% proportion246
Small audience
95%, 5%, 50%, population 300169
Need the guide or a nearby tool?
Need a slower walkthrough, a related calculator, or the full library? These links keep you close to the task you started.
- How to use the Sample Size CalculatorSee slower examples, input meanings, formula notes, result limits, and mistakes to avoid.
- CalculatorsBrowse related calculators and utilities in the same category.
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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 do the main Sample Size Calculator inputs mean?
Confidence level controls the z-score, margin of error is the plus-or-minus percentage you can tolerate, population proportion is the expected yes/share percentage, and optional population size applies finite population correction.
Should I enter 5 or 0.05 for margin of error?
Enter percentages as whole percent values. For a 5% margin of error, type 5. For an expected 20% response proportion, type 20.
How should I read the Sample Size Calculator answer?
The required sample size is the completed response count after rounding up. Raw n is the open-population estimate, and adjusted n shows the finite-population corrected value when you enter a population size.
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.
Why does 50% give the largest sample size?
A 50% proportion has the most uncertainty for a yes/no estimate. Proportions closer to 0% or 100% have less spread, so the formula usually needs fewer responses.
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.
Why does a smaller margin of error need more responses?
A tighter margin of error asks the survey to estimate the true proportion more precisely. Precision costs sample size, so moving from 10% to 5% margin usually increases the required responses a lot.
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.
What should I double-check before trusting the Sample Size Calculator?
Check that your sample will be reasonably random or representative, that you planned for nonresponse, that subgroups have enough responses, and that design effects or weighting are not needed for your survey method.
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.