Explore standard normal distribution probabilities, Z-scores, percentiles, and confidence levels with an interactive Z-table calculator and reference guide.
Z-Table Calculator with Normal Distribution Curve
Standard Normal Distribution
The shaded area represents the selected normal probability.
One Z-Score Probability
Results
What this result means
View Step-by-Step Solution
What Is a Z-Score?
A Z-score measures how many standard deviations a value is above or below the mean.
- x = observed or raw value
- mu = population mean
- sigma = population standard deviation
Common Critical Z-Values
Two-sided critical values for common confidence levels.
| Confidence | Two-sided critical Z |
|---|---|
| 80% | +/-1.282 |
| 90% | +/-1.645 |
| 95% | +/-1.960 |
| 98% | +/-2.326 |
| 99% | +/-2.576 |
| 99.9% | +/-3.291 |
Cumulative Z-Table
This table shows cumulative area to the left of a positive Z-score.
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Published: August 27, 2026
Last Updated: September 6, 2026
