# How to calculate Specular value for Principled BSDF node from IOR?

With regard to the manual the Specular value for the new Principled BSDF node can be computed with following formula:

$\text{specular}=\left(\frac{\text{ior}-1}{\text{ior}+1}\right)^2/0.08$ For example:

water: ior = 1.33, specular = 0.25
glass: ior = 1.5, specular = 0.5
diamond: ior = 2.417, specular = 2.15


But I am getting other numbers. Is the formula wrong? If so, what is the correct one?

• The formula works for me, I get the same results. Are you maybe doing a sqrtf() instead of sqr()? Jul 19, 2017 at 13:27
• Yes... I was using square root by mistake. Thanks for pointing that out. It works perfectly. Jul 19, 2017 at 15:04