Physical height calculation of RA surface finishes.

[billing]

Ra or RMS surface finishes are computed by the profilometer as root mean square results.
Does anyone know a source for the physical height of the " peak to valley " that is being represented as Ra?
I am sure there is a math formula for this but my search has not discovered it. Just the formulae would be good, but a calculator would be awsome :-)... TIA

[Kelly_Bramble]

See the following webages, bottom gives references:

• Surface Finish Roughness Metrology Tutorial
• Surface Roughness Conversion Chart Tables
• Surface Roughness (Finish) Review and Equations