To try to help the OP with her question -

On a modern rapier loom 12 oz Poly/Rayon fabric has about 26 ends per cm or 66 per inch
13oz wool fabric has approx. 17-18 ends per cm or 68 per inch.
and 16oz wool fabric has about 14.5 ends per cm or 57 per inch.

This is using the weaving method where larger yarns are used to achieve the different weights.
Some weavers use the same yarns but increase or decrease the number of ends per inch to achieve the desired weights.

In the end the only things that matter are;

That the fabric has a good kilt selvedge.
That the fabric follows the published thread counts for the desired Tartan.
And that the fabric is the desired weight per linear yard. (1 fabric yard = 54" to 60' wide X 36' long)

A nice tight twill weave is also a sought after quality although plain weaves were used historically.

I hope this helps.