Under Armour Cable Diameter

Options:

1. If the type number and manufacturer are known, consult the manufacturer.
2. If it is manufactured to a known standard, consult the standard.
   
3. If a sample is available, measure it.

Otherwise it's anyone's guess.

How we can know the under armour cable diameter of cable if we know the over all diameter ?

It can vary depending on the cable type and armour type.

This information is generally supplied in the data sheet for the cable. Do you know the cable manufacturer and cable type, this should be enough for you to download the data sheet off the manufacturers website.

If this is a custom built cable for a job, and you don't have the job reference to go back to the manufacturer with for them to give you the cable data sheet then your options are to either guess (by looking at similar cable data sheets) or if it is more critical, then actually measure (if you have access to the cable).