What Is My Z Score?
"My z score" is a request for a comparison: your value, measured against your group's average, in the group's own units of spread. You need exactly three numbers — your value X, the group mean μ, and the group standard deviation σ — and the answer takes one line of arithmetic.
The recipe: z = (your value − group mean) ÷ group standard deviation. Then read the percentile from the table to hear the answer in plain language: "I stand higher than about __% of the group." The finder below converts your z to that percentile with the region shaded.
The slider starts at 1.96 — the most-used value in statistics: it marks the edge of the middle 95% of values.
Values generated from the standard normal cumulative distribution · Verified November 2026
Three personal examples
- An exam result. You scored 78; the class mean is 65 with σ = 9. z = (78 − 65) / 9 = 1.44 — the 92.51st percentile. In a class of 120, roughly 9 students scored higher. (Bring your own class's published mean and spread; "the class" is the only honest reference group for this question.)
- Height. A woman of 172 cm against a female reference mean of 162 cm, σ = 7 cm: z = (172 − 162) / 7 = 1.43, the 92.36th percentile — taller than about 92% of the reference population. Growth and health charts are built on exactly this computation, with the reference matched by age and sex.
- A 5k run — where lower wins. You run 26 minutes; your club's mean is 30 with σ = 4. z = (26 − 30) / 4 = −1.00. The percentile reads 15.87th — but for times, the small side is the fast side: only about 16% of the club is quicker... precisely, your time beats 84% of the club. The z formula does not know which direction is good; you supply that judgement, as the interpretation guide insists.
Where do I get the mean and standard deviation?
That is the real difficulty behind this question — not the arithmetic. Exam boards and testing agencies publish them (or the percentile directly). Fitness and health references come from population studies, and your device apps increasingly report percentiles natively. If you have raw group data — a class spreadsheet, a season of race results — compute μ and σ from it, or use a rough σ estimate: for roughly bell-shaped data, (max − min) / 6 approximates σ well enough for a personal answer. What you cannot honestly do is invent a reference group after seeing your value: a z score is only ever as meaningful as the group it names. For the underlying method with more scenarios, the calculation guide is the full treatment.
Also asked as: what is my z · how do I find my z score · what is my z-score · find my z score.
Related questions
Frequently asked questions
Is my z score the same as my percentile?
No — the z score is the position in standard-deviation units; the percentile is the same position as a rank out of 100. Convert with the table or the finder above. The comparison page explains why both exist.
My group's data isn't bell-shaped. Does my z score still mean anything?
The arithmetic still runs, but the percentile translation assumes the normal curve. For skewed groups (incomes, race times at elite level), the z score remains a fair "distance from average" measure while its percentile should be read from the actual data instead of the table.