Statistics Calculators

Critical Value Calculator (t or z)

Calculate the z or t critical value for a chosen confidence level, tail type and (for t) degrees of freedom.

Critical value —

About the Critical Value Calculator (t or z)

A critical value is the cutoff point on a distribution beyond which a test statistic is considered statistically significant. This calculator finds it for either the standard normal (z) distribution or Student's t-distribution.

Formula: Z critical values are fixed constants (1.645, 1.96 or 2.576 for two-tailed 90/95/99%) · T critical values are approximated from the z value using the Cornish–Fisher expansion, adjusted for degrees of freedom

Use the t-distribution when the population standard deviation is unknown and the sample is small; as degrees of freedom increase, the t critical value converges toward the z critical value.