FREE INTERACTIVE TOOL
Sample Size Calculator
Calculate how many participants your study needs — with power analysis built in and an APA-style reporting paragraph ready to use.
BEFORE YOU START — FOUR THINGS TO HAVE IN MIND
1
Your planned statistical test
Know which test you plan to use — use the Stats Selection Tool first if you are unsure.
2
Your effect size
You need an estimate of the effect size you expect to find. Check previous research or use Cohen's benchmarks for small, medium, or large effects.
3
Your significance level
This is usually .05 for most research. Some disciplines — particularly health and medical research — use .01.
4
Your power level
Most researchers use .80 as a minimum. Some disciplines recommend .90. Check the conventions in your research area.
Not sure about effect size? Use the Effect Size Calculator first →
ABOUT THIS TOOL
How the Sample Size Calculator works
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The Sample Size Calculator helps you estimate how many participants your study needs before you begin collecting data. It guides you through the key decisions involved in sample size planning — the statistical test you expect to use, the effect size you anticipate, the significance level you will adopt, and the level of statistical power you want to achieve.
The calculator covers the most commonly used statistical tests including t-tests, ANOVA, correlation, regression, and chi-square. For more complex designs or formal grant applications, a specialised power analysis program such as G*Power is recommended.
This calculator is intended as a planning guide only. The estimate should always be considered in light of your study design, the assumptions you have made, and the conventions in your discipline. For more complex analyses or formal power analysis, use a specialised program such as G*Power or seek statistical advice.