Power Analysis and Sample Size Calculator
Find the sample size you need to detect an effect with the power you want. Calculations use noncentral distributions and match G*Power.
Updated · By Bibin XavierData 10 × 4
| Studytext · 10 levels | Effect_Size_dnumeric | SEnumeric | Nnumeric |
|---|---|---|---|
| Adams 2015 | 0.05 | 0.13 | 238 |
| Bose 2016 | -0.06 | 0.22 | 81 |
| Chen 2017 | 0.31 | 0.12 | 285 |
| Duarte 2018 | 0.18 | 0.15 | 177 |
| Eriksen 2018 | 0.25 | 0.13 | 229 |
| Fofanah 2019 | 0.75 | 0.31 | 41 |
| Gupta 2020 | 0.01 | 0.28 | 51 |
| Halvorsen 2021 | 0.14 | 0.2 | 97 |
Variables and options
Results
Calculated in your browserPower by sample size
Sample size by power
| Power | n per group | Total N |
|---|---|---|
| 0.80 | 64 | 128 |
| 0.90 | 86 | 172 |
| 0.95 | 105 | 210 |
Interpretation
To detect d = 0.5 with 80% power at α = 0.05 (two-tailed), you need 64 participants per group, 128 in total. Add 10–20% to allow for dropout.
How to cite this tool
Using these results in a thesis, journal article, report or class assignment? Please cite this free tool so others can find it. It keeps the site free.
APA 7
Xavier, B. (2026). Power Analysis and Sample Size Calculator [Web application]. FreeStatisticalTools.com. https://freestatisticaltools.com/power-analysis-sample-size-calculator/
BibTeX
@software{xavier_poweranalysis_2026,
author = {Xavier, Bibin},
title = {Power Analysis and Sample Size Calculator},
publisher = {FreeStatisticalTools.com},
year = {2026},
url = {https://freestatisticaltools.com/power-analysis-sample-size-calculator/},
note = {Web application}
}Suggested sentence for your methods section: “The analysis was carried out with the free Power Analysis and Sample Size Calculator tool on FreeStatisticalTools.com (Xavier, 2026).”
What is a power analysis?
A priori power analysis finds the sample size needed to detect an expected effect with the desired power. Calculations use noncentral t, F and chi-square distributions and match G*Power.
When to use a power analysis
Run it before collecting data to justify your sample size, as most ethics boards and grant reviewers require.
How to use this calculator
- Enter the values. Fill in test, effect size d, significance level α and desired power.
- Read the results. Results update automatically. Read the plain-English interpretation, then use Copy table to paste APA-style tables into Word and Copy for the results sentence.
How to report a power analysis in APA style
“A power analysis indicated that 128 participants (64 per group) were needed to detect a medium effect (d = 0.5) with 80% power at α = .05.”
Frequently asked questions
What power should I aim for?
80% is the conventional minimum; 90% is increasingly expected for confirmatory studies and grant applications.
How do I choose an effect size?
Use the effect from a pilot study, meta-analysis or similar studies. If none exists, Cohen’s small, medium and large benchmarks are a starting point.
Should I add extra participants for dropout?
Yes. Inflate the calculated sample size by your expected attrition rate, typically 10–20%.
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