Z Critical Values Table for Common Confidence Levels
A central 95% standard normal interval uses ±1.959964, usually rounded to ±1.96.
For a central two-sided interval with coverage C, α = 1 − C and z* = Φ⁻¹(1 − α/2). The one-sided column is the upper quantile Φ⁻¹(C). Select the column matching your intended one-sided or two-sided use.
| Coverage C | α = 1 − C | Two-sided ±z* | One-sided upper z* |
|---|---|---|---|
| 80% | 0.2 | 1.281552 | 0.841621 |
| 90% | 0.1 | 1.644854 | 1.281552 |
| 95% | 0.05 | 1.959964 | 1.644854 |
| 98% | 0.02 | 2.326348 | 2.053749 |
| 99% | 0.01 | 2.575829 | 2.326348 |
| 99.9% | 0.001 | 3.290527 | 3.090232 |
These are standard normal quantiles, not Student’s t critical values. A confidence interval for an estimated mean may require a t distribution depending on its assumptions.