I think it was much easier when the world wasn’t made out of polyester...every fabric had a name and was fairly consistent.
Thats so very true.
That link gives fabric weights in gsm and osy, and the needle sizes in metric and imperial/USA sizes but the thread weights are all related to cotton thread and cotton count (number of 840 yard hanks obtained from 1 lb fibres). Poly threads, if they have a number on the spool, are usually measured by the metric number, Nm which is the number of 1,000 metre hanks obtained from 1Kg fibres.