# Statistical Power Calculator Estimate statistical power for one-sample mean or proportion tests using sample size, alpha, and expected effect > Canonical page: https://elysiatools.com/en/tools/statistical-power-calculator - **Category:** Math & Numbers - **Keywords:** statistical power, hypothesis test, sample size, alpha, effect size, calculator ## Overview The Statistical Power Calculator estimates the probability of correctly rejecting a false null hypothesis for one-sample mean or proportion tests. By inputting your sample size, significance level (alpha), and expected effect size parameters, you can quickly determine the statistical power of your study design and ensure your experiments yield reliable results. ## Inputs - **Test Type** (select) - **Alternative Hypothesis** (select) - **Significance Level** (number) - **Sample Size** (number) - **Null Mean** (number) - **Alternative Mean** (number) - **Standard Deviation** (number) - **Null Proportion** (number) - **Alternative Proportion** (number) - **Decimal Places** (number) ## When to use - When planning a study and needing to verify if a predetermined sample size provides sufficient power to detect an expected effect. - When evaluating the feasibility of a one-sample mean or proportion test before collecting data. - When conducting post-hoc analysis to understand the statistical power of a completed experiment given the observed sample size. ## How it works - Select the test type (Mean Difference or Proportion Difference) and the alternative hypothesis direction (two-sided, greater, or less). - Enter your study parameters, including the significance level (alpha), sample size, and the null and alternative values. - Provide the standard deviation for mean tests, or adjust the proportion values for proportion tests. - The calculator computes the effect size and returns the estimated statistical power as both a probability and a percentage. ## Use cases - Academic researchers verifying study designs to ensure adequate power before submitting grant proposals. - Data analysts evaluating whether a fixed sample size in an A/B test is sufficient to detect a specific conversion rate change. - Quality control engineers determining if a sample batch size is large enough to detect deviations from a target manufacturing mean. ## Frequently asked questions ### What is statistical power? Statistical power is the probability that a hypothesis test will correctly reject a false null hypothesis, effectively avoiding a Type II error. ### What is considered a good statistical power level? A common standard in many scientific and business fields is 0.80 (or 80%), meaning there is an 80% chance of detecting an effect if one genuinely exists. ### How does sample size affect statistical power? Generally, increasing the sample size increases statistical power, making it easier to detect a true effect because it reduces the standard error. ### What is the difference between a one-sided and two-sided test? A two-sided test checks for differences in both directions (greater or less than the null), while a one-sided test only looks for a difference in one specific direction. ### Can I calculate power for proportions? Yes, select 'Proportion Difference' as the test type and input your null and alternative proportions to calculate the power. ## Related tools - [Average Calculator](https://elysiatools.com/en/tools/average-calculator): Compare arithmetic, geometric, and harmonic averages for a numeric dataset in one place - [Confidence Interval Calculator](https://elysiatools.com/en/tools/confidence-interval-calculator): Calculate confidence intervals for a sample mean or proportion using either raw data or summary statistics - [Geometric Mean Calculator](https://elysiatools.com/en/tools/geometric-mean-calculator): Calculate the geometric mean of positive numeric values for growth rates, ratios, and multiplicative datasets - [Heat Exchanger LMTD Calculator (Log Mean Temperature Difference)](https://elysiatools.com/en/tools/heat-exchanger-lmtd): Compute the Log Mean Temperature Difference (LMTD) of a heat exchanger for parallel or counter flow. 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