Free interactive student tool
Free Sample Size and Power Calculator
Free Sample Size and Power Calculator. Separate survey estimates from experimental power calculations; document each formula.
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Planning approximation
How this tool reaches its result
The calculator provides common normal-approximation estimates for a proportion or two-group standardized effect.
Planning approximation
Worked context
How to interpret the output
A 95% confidence estimate for an unknown proportion commonly uses p = .50 for a conservative sample size.
Important limitation
What the result cannot decide for you
Clustered designs, attrition, finite populations and complex models require specialist adjustments.