Stanford–Binet scale: history, SD, and interchangeability

This is an educational scale note, not a Stanford–Binet test and not a place to take one. IQ Caddy converts already-standardized scores on a mean-100, SD-15 model.

Deviation IQ, not a quiz

Modern IQ scores are usually deviation scores: a standing versus a reference group, centered near 100. Early ratio IQ used mental age divided by chronological age. That historical formula is explained on average IQ by age. It is not how this site’s calculator works.

SD 16 versus SD 15

Some historical Stanford–Binet editions used a standard deviation of 16. Many current instruments, including Wechsler-style scales and Stanford–Binet Fifth Edition, use SD 15. The same z-score therefore prints as a different IQ if σ changes:

x₂ = 100 + ((x₁ − 100) / σ₁) × σ₂

Example: 130 on SD 15 is z = 2. On SD 16 that same z prints as 132. The converter shows that arithmetic. It does not claim the two tests measured the same thing.

What this page will not do

• It will not administer items or estimate your IQ.
• It will not sell or link a fake “Stanford–Binet online test.”
• It will not treat SD 16 as the current Stanford–Binet rule for every edition.

Questions

What is the Stanford–Binet scale?

It is a standardized intelligence scale with a long edition history. This page explains scoring conventions. IQ Caddy does not administer the Stanford–Binet or any publisher’s test.

Does Stanford–Binet use SD 16?

Some historical Stanford–Binet editions used a standard deviation of 16. Current Wechsler scales and Stanford–Binet Fifth Edition use SD 15. Do not treat every printed “Stanford–Binet IQ” as SD 16.

Can I convert a Wechsler IQ to Stanford–Binet?

You can rescale a z-score if you assume both numbers are deviation IQs with known means and SDs. That does not reproduce either publisher’s norms, age tables, or score report.

Related: percentile calculator, methodology, IQ scale and chart.