Quick start
- Choose a confidence level.
- Enter the margin of error as a percentage.
- Enter the estimated population proportion, often 50% when unknown.
- Add a finite population size only when the population is limited.
Best uses
Start here if one of these sounds like your job. The examples below show which inputs matter most.
- 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.
What the inputs mean
Higher confidence levels usually require a larger sample. Smaller margins of error also require a larger sample.
The estimated proportion is the expected percent of people with the answer or trait you are measuring. If you do not know it, 50% is the conservative default.
Finite population correction
If the total population is small and known, enter it to apply a finite population adjustment.
If the audience is very large or unknown, leave population size blank and use the standard large-population estimate.
Worked examples for Sample Size Calculator
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FAQ in plain language
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 do the main Sample Size Calculator inputs mean?
The main inputs are the numbers, operation, mode, or known values the calculator needs. Keep units consistent, enter percentages the way the page label shows, and use the examples as a quick check before trusting the answer.
How should I read the Sample Size Calculator answer?
Read the headline answer, then check the supporting lines and examples to understand how the calculator got there. If one input changes, rerun the tool and compare the new answer instead of guessing.
What should I double-check before trusting the Sample Size Calculator?
Check units, signs, rounding, and the selected mode before copying the answer. If the number feels weird, rerun one of the examples first, then put your own values back in slowly.
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.
Sources
Use these if you want to compare the formula, inputs, or limits with a trusted outside explanation.
Related tools
- Confidence Interval Calculator Calculate z confidence intervals for a mean or a proportion.
- Probability Calculator Calculate event union, intersection, complements, and independent-event probability.
- Statistics Calculator Calculate count, sum, mean, median, mode, range, quartiles, variance, and standard deviation.
Keep exploring
If this guide is close but not exact, these links keep you near the same kind of problem.
- Calculators Browse the full category for related tools that help with the same job.
- All free tools Search the complete Access Free Tools library by task, category, or tool name.
- All calculator and utility guides Find more plain-language examples, formulas, mistakes, and result explanations.
- Free calculator resources Start here when you are not sure which calculator page fits.
Privacy and copying results
Recent answers stay visible only while you work in the current browser tab. They are not sent to a server.
Use Copy answer when you want to save the inputs and result in notes, homework, a message, or a project list. Check the units, labels, and limits before copying.