Z-Score Calculator
Standardises a value so it can be compared with values from other scales.
Share sends a link that reopens these numbers. Copy details pastes the full breakdown as a list.
The formula
z = (x − μ) ÷ σ T = 50 + 10z
A z-score puts values from different scales on one common scale. A standardised T-score, used for some test scores, is the same thing rescaled to a mean of 50 and a standard deviation of 10.
What to watch out for
Positive means above the mean and negative means below. Student’s t statistic is a different quantity, and has its own calculator.
Frequently Asked Questions
What does a z-score of 1.96 mean?
It is 1.96 standard deviations above the mean. In a normal distribution 97.5% of values fall below it.
What z-score is the 90th percentile?
1.282, in a normal distribution.
What is a good T-score?
A T-score of 50 is exactly average, and 60 is one standard deviation above, or about the 84th percentile if normal.