P-value calculator
Get p-value from z for one-tailed or two-tailed test
P-value — probability of observing a result as or more extreme than the one obtained, if the null hypothesis is true. From z-score.
Parameters
Standardized deviation from the mean
Assumptions and limitations
- z = 1.645 → p = 0.10 (two-tailed)
- z = 1.96 → p = 0.05 (two-tailed)
- z = 2.576 → p = 0.01 (two-tailed)
P-value
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Enter z-score
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1 z = 1.96 (two-tailed)
95% confidence boundary
p ≈ 0.05 — at the significance boundary; at α = 0.05 the result is considered significant.
2 z = 2.5 (two-tailed)
Stronger deviation
p ≈ 0.012 — significant at α = 0.05 and α = 0.01; stronger evidence against the null hypothesis.
3 z = 3 (two-tailed)
Very strong deviation from H0
p ≈ 0.003 — high confidence in rejecting the null hypothesis.
4 z = 1.0 (two-tailed)
Weak deviation
p ≈ 0.32 — not significant at α = 0.05; the result could easily have occurred by chance.
5 z = 2.576 (two-tailed)
99% confidence boundary
p ≈ 0.01 — significant at α = 0.01; used for stricter conclusions.
6 z = 1.65 (one-tailed)
One-tailed test: only "greater" or only "less"
p ≈ 0.05 — for one-tailed the significance boundary at α = 0.05 corresponds to a smaller |z| than for two-tailed.
Frequently asked questions
What is p-value?
When to use two-tailed vs one-tailed?
What is z-score?
Why is 0.05 the standard threshold?
Is p-value = 0.05 significant?
What p-value is NOT?
How to convert z-score to p-value?
When do you need a separate p-value calculator from A/B?
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