T Test Sample Size Calculation

Introduction: The T Test Sample Size Calculator aids researchers in determining the appropriate sample size for a t-test, ensuring the study’s statistical power to detect meaningful effects.

Formula: The calculator employs the formula based on Cohen’s d, alpha (significance level), power, and sides (two-sided or one-sided), yielding the optimal sample size.

How to Use:

  1. Input the effect size (Cohen’s d).
  2. Specify the significance level (α).
  3. Specify the desired statistical power.
  4. Choose between two-sided or one-sided test.
  5. Click the “Calculate” button to obtain the required sample size.

Example: For instance, with an effect size of 0.5, significance level of 0.05, power of 0.8, and a two-sided test, the calculator may yield a recommended sample size of 64.


  1. What is Cohen’s d effect size?
    • Cohen’s d quantifies the standardized difference between two means, providing a measure of practical significance.
  2. Why is statistical power important?
    • Statistical power represents the probability of detecting a true effect, minimizing the risk of Type II errors in hypothesis testing.
  3. What is a two-sided test vs. one-sided test?
    • In a two-sided test, the researcher examines if there is a significant difference in either direction, while a one-sided test focuses on a difference in a specific direction.

Conclusion: The T Test Sample Size Calculator enhances experimental design by ensuring that studies have an adequate sample size to detect meaningful effects with appropriate statistical power. Researchers can optimize their resources and maximize the reliability of their findings.

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