Sample Size and Power Calculators
Sample Size for Two Proportions Calculator
Sample Size for Two Proportions Calculator estimate sample size for comparing proportions.
Sample Size and Power Calculators
Sample Size for Two Proportions Calculator
Estimate sample size for comparing proportions.
Formula
Two independent proportions sample size uses the normal approximation with pooled planning proportion for alpha and separate group variances for power.
About the Sample Size for Two Proportions Calculator
Estimate sample size for comparing proportions. Planning calculators connect effect size, precision, alpha, power, group count, and sample size for the specific design shown.
How the Sample Size for Two Proportions Calculator Works
Two independent proportions sample size uses the normal approximation with pooled planning proportion for alpha and separate group variances for power.
The calculation runs in your browser. Submitted values are validated for the required numeric range, data shape, units, and method-specific restrictions before a result is shown.
Required Inputs
- Proportion A (required)
- Proportion B (required)
- Target power (required)
- Alpha (required)
Results Reported
The result panel shows the final answer together with the intermediate quantities needed to audit the calculation. Depending on this method, reported values include:
methodproportion_aproportion_bproportion_differencepooled_planning_proportionalphatarget_powerz_alphaz_powerunrounded_sample_size_per_grouprequired_sample_size_per_grouptotal_sample_size
Sample Size for Two Proportions Calculator Example
Use the example data button to load a known sample, then calculate and review the statistic, p-value or estimate, and interpretation.
| Input | Example value |
|---|---|
| Proportion A | 0.50 |
| Proportion B | 0.65 |
| Target power | 0.80 |
| Alpha | 0.05 |
How to Use the Calculator
- Confirm that the calculator title and method match the quantity, test, conversion, or planning question you need to solve.
- Enter values with compatible units and the requested sample, group, matrix, count, date, or option format.
- Select Example Data to inspect a valid input layout, or enter your own values and select Calculate.
- Review the result table, formula, worked substitutions, warnings, and interpretation rather than using only the headline number.
- Use Copy Result or Download CSV when you need a reusable record of the displayed calculation.
Understanding the Result
Planning assumptions should be justified before data collection; attrition, clustering, unequal allocation, and multiplicity may require a larger design.
Keep the entered values, units, selected options, and any warning shown beside the result. For a hypothesis test, report the statistic, degrees of freedom where applicable, p-value, alpha level, effect size, and decision. For an estimate or conversion, report the formula convention and final unit.
Accuracy and Limitations
The calculator keeps full browser precision during calculation and rounds only for display. Accuracy still depends on correct inputs and on whether the displayed model represents the real problem. Educational calculators cannot replace required professional review, current official rules, field measurements, laboratory methods, or specialist statistical software where those are necessary.
Frequently Asked Questions
What does the Sample Size for Two Proportions Calculator calculate?
Estimate sample size for comparing proportions.
Which formula does the Sample Size for Two Proportions Calculator use?
Two independent proportions sample size uses the normal approximation with pooled planning proportion for alpha and separate group variances for power.
What input does this calculator need?
The calculator form shows the required values and validates them before calculating.
Are the formulas visible?
Yes. Each calculator displays its method, assumptions, and interpretation unless disabled by the site administrator.