Sample Size Calculator
This free sample size calculator determines the sample size required to meet a given set of constraints.
How to Use the Sample Size Calculator
Enter confidence level, margin of error, and population assumptions to estimate required survey sample size.
Precision Planning
Sample-size design balances confidence and error tolerance objectives.
Conservative Assumptions
Unknown proportions often use p=0.5 for worst-case variance.
Population Adjustment
Finite correction becomes relevant when sampling fraction is large.
Operational Reality
Recruitment losses should be included in fieldwork sample targets.
Method Boundaries
Formula outputs are reliable only when underlying assumptions hold.
Frequently Asked Questions
What is sample size?+
Sample size is the number of observations needed for target precision.
How does confidence level affect n?+
Higher confidence usually requires larger sample sizes.
How does margin of error affect n?+
Smaller margin requires larger sample sizes.
What is p in sample-size formula?+
p is expected proportion; 0.5 is conservative when unknown.
Does population size always matter?+
For very large populations, its effect is often limited.
What is finite population correction?+
An adjustment that can reduce required n for small populations.
Can nonresponse inflate needed sample?+
Yes, practical recruitment plans should account for nonresponse.
Is random sampling assumed?+
Yes, standard formulas assume representative random sampling.
Can this guarantee unbiased results?+
No, design quality and data collection still determine bias risk.
Is this only for binary outcomes?+
Common formula targets proportions; other designs use different methods.
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