A z-score (standard score) measures how many standard deviations a value is from the mean of a distribution. A z-score of 0 is exactly average; +1 is one SD above average (84th percentile).

A T-score is a scaled score with a mean of 50 and a standard deviation of 10. It avoids negative numbers and decimals. T = 50 + 10z.

How are stanines calculated?

Stanines (standard nines) run from 1 to 9 with a mean of 5 and SD of 2. They divide the normal curve into 9 bands: stanines 1–3 are below average, 4–6 average, and 7–9 above average.

What is an NCE score?

Normal Curve Equivalent (NCE) scores have a mean of 50 and SD of 21.06. Unlike percentiles, they are equal-interval, which makes them useful for statistical comparisons in educational research.

What is a standard score with mean 100 and SD 15?

This scale is used for IQ tests (Wechsler, Stanford-Binet). A score of 115 equals a z-score of +1 (84th percentile); 85 equals a z-score of -1 (16th percentile).

Why do percentile ranks and standard scores differ?

Percentile ranks are not equal-interval — the difference between the 50th and 60th percentile is smaller than between the 80th and 90th. Standard scores are equal-interval, making them better for arithmetic comparisons.

Standard Score Converter

Name: Standard Score Converter
Availability: InStock
Author: Nham Vu

Enter any standard score type and instantly convert to z-score, percentile rank, T-score, stanine, and NCE equivalents.

Enter a Score

Score Type

Score Value

Classification Reference

Range	Percentile	Label
130+	≥ 98th	Very Superior
120–129	91–97th	Superior
110–119	75–90th	High Average
90–109	25–74th	Average
80–89	9–24th	Low Average
70–79	2–8th	Borderline
≤ 69	≤ 1st	Extremely Low

Based on IQ / SS scale (mean=100, SD=15).

Enter a score and click Convert to see equivalents.

Summary

Enter any standard score type and instantly convert to z-score, percentile rank, T-score, stanine, and NCE equivalents.

How it works

Select the score type you want to convert from (e.g., z-score, T-score, IQ, stanine, NCE, or percentile).
Enter your score value in the input field.
The tool calculates the equivalent z-score using the known mean and standard deviation for that scale.
The normal distribution CDF converts the z-score to a percentile rank.
All equivalent score types are displayed simultaneously in the results panel.

Use cases

Interpret standardized test results from school psychologist reports.
Compare scores across different assessment instruments (e.g., IQ vs. achievement tests).
Understand where a student falls relative to peers using percentile rank.
Convert z-scores from research data into more intuitive T-scores or stanines.
Explain assessment results to parents or students in plain terms.
Cross-reference scores from different norm-referenced tests in IEP meetings.

Frequently Asked Questions

Last updated: 2026-06-10 · Reviewed by Nham Vu