Compare calculators

Both calculators run independently — change the inputs on either side to compare results.

Statistical Power Calculator

Calculates the statistical power of a hypothesis test or the sample size needed to detect a given effect. Use it when designing experiments to ensure your study can reliably detect meaningful differences.

Effect Size (Cohen's d)

Significance Level (α)

Sample Size (per group) (participants)

Calculate

Fill in the required fields to see your result.

Probability

Birthday Paradox Calculator

Calculate the probability that at least two people in a group share a birthday. Useful for teaching probability concepts or settling that classic party debate.

Group Size (Number of People)

Days in Year

Calculate Probability For

Result Format

Fill in the required fields to see your result.

Key differences

	Statistical Power Calculator	Birthday Paradox Calculator
Category	Probability	Probability
Inputs required	4	4
Result	Statistical Power	Result
What it does	Calculates the statistical power of a hypothesis test or the sample size needed to detect a given effect. Use it when designing experiments to ensure your study can reliably detect meaningful differences.	Calculate the probability that at least two people in a group share a birthday. Useful for teaching probability concepts or settling that classic party debate.