Calculate sample sizes for each stratum in a stratified random sampling design. Enter your total population size, desired total sample size, and up to six strata with their population proportions — the calculator returns the sample size per stratum using proportional allocation, plus a breakdown chart and summary table.
Total Sample Size
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Sampling Fraction
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Number of Active Strata
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Total % Allocated
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Stratified random sampling is a method where you divide your total population into distinct subgroups called strata (e.g. by age, gender, or region) and then draw a random sample from each stratum. This ensures every subgroup is represented in the final sample, making results more reliable and representative than simple random sampling.
Proportional allocation assigns sample sizes to each stratum in proportion to its share of the total population. If a stratum makes up 30% of the population and your total sample size is 200, it receives 60 samples. This calculator uses proportional allocation by default, which keeps the sample representative of the overall population.
Equal allocation divides the total sample size evenly across all strata, regardless of their population sizes. This is useful when you want to make reliable estimates for each stratum independently — for example, when comparing small and large groups side by side. It can, however, produce estimates that are less efficient for the overall population.
Yes — for the calculation to be valid, all active stratum percentages should sum to 100%. If they do not, the calculator will flag the discrepancy in the 'Total % Allocated' output field. You should adjust your percentages until they total 100% before using the sample size results.
Your total sample size depends on your desired confidence level, margin of error, and population variability. A standard approach for proportions is to use a simple random sample size formula first (e.g., n = Z²·p·(1−p)/e²) and then apply stratification. Online sample size calculators can help you derive a starting value before distributing it across strata.
The current tool supports up to six strata. For surveys with more subgroups, you can apply the same proportional allocation formula manually: for each stratum, multiply your total desired sample size by that stratum's proportion of the population (stratum size / total population).
The sampling fraction is the ratio of your total sample size to the total population size, expressed as a percentage. It tells you what share of the population you are surveying. A sampling fraction above 5–10% is considered large and may warrant finite population corrections in your statistical analysis.
In stratified sampling, you divide the population into strata and sample from every stratum. In cluster sampling, you divide the population into clusters and randomly select only some clusters to survey entirely. Stratified sampling generally gives more precise estimates but requires knowledge of stratum membership for every individual in the population.