T-Score and Critical Value Calculator
A t statistic measures how far a sample mean is from a comparison value, in standard errors.
t statistic
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Degrees of freedom —
Critical t, two-sided —
Standard error —
p-value, two-sided —
Reading this —
The formula
t = (x̄ − μ₀) ÷ (s ÷ √n) degrees of freedom = n − 1
The critical value comes from Student’s t distribution.
What to watch out for
“T-score” also means a standardised score with a mean of 50, used on some tests. That figure is on the z-score calculator.
Frequently Asked Questions
What is the critical t value for 95% confidence and 10 degrees of freedom?
2.228, two-sided. With 30 degrees of freedom it falls to 2.042, and it approaches 1.96 as they increase.
When do I use t instead of z?
Use t when the standard deviation is estimated from the sample, which is nearly always. Use z when the population’s standard deviation is truly known.