Z-Score Calculator
Convert values to z-scores and find probabilities under the normal curve.
Z-score
2
Percentile
97.7%
Share above
2.3%
Standardizing a value
A z-score restates a value in standard deviations from the mean: (x − μ) ÷ σ. An IQ of 130 with μ=100, σ=15 is z = 2 — the 97.7th percentile. Z-scores let you compare across different scales: a 2-SD result is equally exceptional on any test.
The empirical rule
In normal data, |z| < 1 covers 68% of values, |z| < 2 covers 95%, |z| < 3 covers 99.7%. Beyond ±3 is rare enough that it usually signals either a genuine outlier or a data error — both worth investigating.
Related calculators
Percentage Calculator
Solve any percentage problem: percent of, percent change, and more.
Fraction Calculator
Add, subtract, multiply, and divide fractions with simplified results.
Scientific Calculator
A full scientific calculator with trig, logs, and exponents.
Random Number Generator
Generate random numbers in any range, with or without repeats.