There is a confusing array of terms used in relation to yarns and weaving. We hope that this collection of explanations will help you better understand what you are looking at but do please get in touch with us if you would like to see additions to this list.
NM and WC - what can these mean!
Yarn counts are the measure of the 'grist' or thickness of a yarn and relate to the length of yarn required to achieve a certain weight. Historically these varied considerably with diverse regional and fibre counts. Most EU yarn millers now use the standard ‘new metric' or NM count in which a count of 1 is a single strand of yarn (un-plied) that is 1000m long and weighs 1kg. If the yarn is plied with another then this is shown as 'count/plies. So a yarn with an NM count of 6/2 is one that has two strands of yarn each with a count of 6, plied together with a ‘resultant' count of 3 (6 divided by 2). 1000m of each of those three ‘resultant' strands weighs 1kg - so 1kg of NM 6/2 is 3000m long. The higher the ‘resultant' number, the finer the yarn.
Some textile artists and craftspeople still work in the original Bradford Worsted Count (WC) in which a count of 1 is a single strand of worsted yarn that measures 560 yards (the amount that could be wound on to a single bobbin in the old mills) and is 1 pound in weight. As with the NM, WC yarn lengths are calculated by determining the ‘resultant' count and then multiplying that by 560yds.
weaversbazaar provide details of both of these counts for each of its worsted yarns - the numbers do get very complicated but we hope this helps explain it a little.
NM= new metric count
This is the universal yarn thickness measure.
WC= worsted count
This is the historical nomenclature for worsted yarn thickness.
wpi/wpc = wraps per inch/wraps per centimetre
This denotes how many yarn diameters cover an inch/cm width. Clearly the higher the number the finer the yarn.
epi/epc = ends per inch/ends per centimetre
This denotes how many warps per inch or centimetre the yarn could be sett at when tapestry or cloth weaving. It is arrived at by halving the wpi/wpc measure since there has to be a space between each warp for the weft. The epi/epc is given for guidance only as setting the warps closer or further apart is often done to get different types of fabric outcomes. See the Janet Phillips' Masterclass research results on loom setts and fabric types for some examples.