Determine to Assume Outer Diameter of Cable for Choosing Cable Gland
The data sheet or manufacturer's selection guide should give the cable's outer diameter. For a given number of conductors, the cable diameter can vary depending on insulation thickness and other construction details.

Many different-size cables could be used in any connector, regardless of the number of pins. The connector datasheet should describe the permissible range of cable sizes, and/or alternative cable glands or clamps available.