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Updated 2026-03-07 UTC
Z Critical Values Table — Common z* for Confidence Levels — GetCalcMaster
Quick z critical values (z*) for common confidence levels and significance levels, plus one‑tailed vs two‑tailed mapping. Includes a p‑value ↔ z reference section.
This page summarizes the most commonly used z critical values (z*) for confidence intervals and hypothesis tests under the standard normal model, including one‑tailed vs two‑tailed conventions.
Educational use only. For small samples or unknown σ, prefer a t critical value instead of z.
Common z* critical values
Two-tailed critical values use z* = Φ^{-1}(1 − α/2). One-tailed critical values use z* = Φ^{-1}(1 − α).
Two-tailed (confidence intervals)
| Confidence | α | z* |
|---|---|---|
| 80% | 0.2 | 1.2816 |
| 90% | 0.1 | 1.6449 |
| 95% | 0.05 | 1.96 |
| 98% | 0.02 | 2.3263 |
| 99% | 0.01 | 2.5758 |
| 99.5% | 0.005 | 2.807 |
| 99.9% | 0.001 | 3.2905 |
One-tailed (directional tests)
| α (one-tailed) | z* |
|---|---|
| 0.1 | 1.2816 |
| 0.05 | 1.6449 |
| 0.025 | 1.96 |
| 0.01 | 2.3263 |
| 0.005 | 2.5758 |
| 0.001 | 3.0902 |
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Last updated: 2026-03-07