P-Value Calculator
Compare an observed mean with a null mean using a known standard deviation and selected tail.
How to use
- 1Enter sample mean, null mean, standard deviation and sample size.
About
The method is explicitly a one- or two-tailed Z test with a normal approximation.
P-value calculator
Calculate a two-sided or one-sided Z-test p-value for a mean with known standard deviation.
z = (observed mean − null mean) ÷ (deviation ÷ √n); the p-value comes from the standard normal distribution.
Enter observed mean, null mean, standard deviation, sample size and test tail.
A small p-value means the data would be unusual if the null mean were true; it is not an effect-size measure.
Practical examples
- A difference of two standard deviations in a two-sided test gives p about 0.0455.
Limitations and notes
- Only a one-mean Z test with a normal approximation is implemented; t and proportion tests are not included.
- Use valid values and keep all units consistent.
How to use
- 1Enter sample parameters.
- 2Choose two-sided, left or right tail.
- 3Review z, p-value and method.
Frequently asked questions
Does a small p-value prove the alternative?
No. It measures compatibility with the null hypothesis; interpretation depends on context and significance level.
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