Compare calculators

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

Sample Size Calculator

Calculate the minimum number of respondents needed to estimate a population proportion within a given margin of error at a chosen confidence level — the standard formula behind almost every survey, poll, and quality audit. Includes the finite-population correction so you can plan surveys of small populations without over-sampling.

Population Size

Confidence Level

Margin of Error (%)

Fill in the required fields to see your result.

Statistics

Statistical Power Calculator

Determine the statistical power of a hypothesis test given effect size, sample size, and alpha level. Use it when designing experiments to confirm you have enough participants to detect a real effect.

Effect Size (Cohen's d)

Sample Size per Group

Alpha Level

Test Direction

Fill in the required fields to see your result.

Key differences

	Sample Size Calculator	Statistical Power Calculator
Category	Statistics	Statistics
Inputs required	3	4
Result	Required Sample Size	Statistical Power
What it does	Calculate the minimum number of respondents needed to estimate a population proportion within a given margin of error at a chosen confidence level — the standard formula behind almost every survey, poll, and quality audit. Includes the finite-population correction so you can plan surveys of small populations without over-sampling.	Determine the statistical power of a hypothesis test given effect size, sample size, and alpha level. Use it when designing experiments to confirm you have enough participants to detect a real effect.