Statistical Power Calculator
A teaching estimate of power for a two-group comparison.
Runs in your browser. Nothing is uploaded — your input is processed on this device and discarded when you close the tab.
Statistical Power Calculator
How to use this tool
- Enter the effect size as Cohen's d, the sample size per group and the significance level.
- Press Generate to see the estimated power as a percentage.
- Use Load sample for d = 0.5, n = 64 per group and alpha = 0.05.
Worked example
With d = 0.5, 64 people per group and alpha = 0.05, the normal-approximation power is about 80.7%, because the noncentrality value is about 2.83 and the critical value is 1.96.
What this tool does not do / Limits
This is a normal-approximation estimate for teaching only. It assumes a two-sided test on roughly normal data with equal group sizes, and it is not a substitute for proper power analysis with dedicated software or a statistician.
Frequently asked questions
What does 80% power mean?
Roughly, that a real effect of the entered size would be detected about 80% of the time under the stated assumptions. It is not a guarantee for any single study.
Why only 0.01, 0.05 and 0.10 critical values?
This teaching version uses the standard critical values for those common levels and falls back to 1.96 for other entries, which is one more reason to treat the output as an approximation.
Related tools
CSV Cleaning Studio
Remove duplicates, fix missing values, standardise dates and export a clean CSV. Your file never leaves your device.
LiveChart Builder
Build charts from CSV data with aggregation, sorting and accessible colour palettes. Export as PNG or SVG.
LiveLength Converter
Convert lengths between metric and imperial units and see the full table of equivalents.
Live