Thread Sizes, Systems and Conversions
All threads and yarns (with the exception of monofilament 'fishing line' threads and some glittery metalised polyester threads) are made by spinning lots of individual fibres together to make a 'singles' yarn which is inherently unbalanced. To make the thread balanced 2, 3, 4 or more singles are then folded (plied) together to make a balanced thread. Occasionally this second spinning is intentionally tight and a second folding/plying takes place to create a very firm but balanced thread.
The size of a thread is indicated by the thickness of one of the 'singles' used to produce it, and modified to indicate the number of plies. There are several systems in use for measuring the thickness of a thread or yarn, and historically many more systems were used, especially in the wool producing areas of Britain.
The direct systems of measurement are:  The indirect systems of measurement are: 


The higher the number the thicker the thread  The higher the number the finer the thread 
With threads measured by an indirect system the number will be divided by the number of plies, ie:
60/2 Nm which means a two ply thread; one 1,000 metre length of each ply will weigh a sixtieth of 1Kg, so a 1,000 metre length of the plied thread will weigh a thirtieth of 1Kg.
30/3 NeC means a three ply thread; one 840 yard length of each ply will weigh one thirtieth of one pound, so 840 yards of the plied thread will weigh one tenth of a pound.
Some manufacturers of cotton threads state the thickness as 2/60s or 3/40s  which means the same as 60/2 or 40/3.
With threads measured by Tex or dTex the number will be multiplied by the number of plies, ie:
Tex 35 x 3 which means a 3ply thread and each 1,000 metres will weigh 105gms
Threads measured by denier do not usually account for the number of plies, ie a 60 denier thread will weigh 60x9000gms per 1,000 metres regardless of whether it is a singles, a 2 ply, 3 ply etc.
Traditionally filament silk and its synthetic substitutes (rayon and nylon) are measured by denier. Cotton and spun silk threads are measured by English cotton count (NeC or CC) and linen threads are measured by English linen count (NeL). The textiles world is slowly moving to the metric count (Nm) and Tex/dTex systems.
Then there is the thorny issue of Ticket numbers!
A ticket number is a manufacturer's way of identifying a thread product but it is not an accurate way of denoting the size/thickness of the thread.Ticket number can be based on cotton count, metric number or tex and it 'assumes' that the thread is 3ply. Thus ticket number 30 could mean a 30/3 thread  or it could be a 20/2 or it could be a 60/6 they each contain the same amount of fibres per metre. Add to that the fact that Tex and Nm sizes are bracketed into groups for ticketing purposes and the size is rounded down to the smallest of the bracketed group. It should come as no surprise that two threads from different manufacturers can each have the same ticket number but be rather different in size.
Because there are so many different systems in use lacemakers and other textile hobbyists have a need to compare the thicknesses of threads and yarns with a single formula.
My'Threads for Lace'book uses the informal wraps per cm system, derived from the wraps per inch used by weavers. It is also fairly easy to measure the tex of a resultant (plied) thread or yarn.

C o n v e r t t o 

Tex  dTex  Denier  Metric No  Cotton No  Linen No  
Tex    Tex x 10  Tex x 9  1,000 ÷ Tex  591 ÷ Tex  1,654 ÷ Tex  
dTex  dTex ÷10    dTex x 0.9  10,000 ÷ dTex  5,910 ÷ dTex  16,540 ÷ dTex  
Denier (den)  den ÷ 9  den ÷ 0.9    9,000 ÷ den  5,314 ÷ den  14882 ÷ den  
Metric No (Nm)  1,000 ÷ Nm  10,000 ÷Nm  9,000 ÷ Nm    0.59 x Nm  1.65 x Nm  
Cotton No (NeC)  591 ÷ NeC  5,910 ÷ NeC  5314 ÷ NeC  NeC x 1.69    NeC x 2.8  
Linen No (NeL)  1,654 ÷ NeL  16,540 ÷ NeL  14,882 ÷ NeL  NeL x 0.60  NeL x 0.36   
Some historical measuring systems 

Direct or fixed length systems  
Denier  weight in gms of 9,000 metres  a single filament of silk is about 1 den  
Tex  weight in gms of 1,000 metres  
dTex  weight in gms of 10,000 metres  
Jute, hemp linen etc (dry spun)  weight in lbs of 14,400 yards  14,000 yards = 1 spyndle = 48 x 300 yard hanks  
Woollen  Aberdeen  weight in lbs of 14,400 yards  14,000 yards = 1 spyndle = 48 x 300 yard hanks  
Woollen US Grain  weight in grains of 20 yards  700 grains = 1 lb, 1 grain = 64.79891 mg  
Indirect or fixed weight systems  
Asbestos (American)  number of 100 yard cuts from 1 lb  
Asbestos (Englsh)  number of 50 yard lengths from 1 lb  
English cotton count  number of 840 yard hanks from 1 lb  CC, NeC or NeB=baumwolle number. Also used for spun silk.  
English linen number (wet spun)  number of 300 yard hanks from 1 lb  1 hank of linen = 300 yards = 1 lea  
Metric Number  number of 1,000 metre lengths from 1 Kg  
Cotton Bump yarn  number of yards from 1 oz  
Glass fibre  number of 100 yard lengths from 1 lb  
Typp  number of 1,000 yard lengths from 1 lb  Thousand Yards Per Pound  
Woollen  Alloa  number of 11,520 yard spyndles from 24 lb  
Woollen  American cut  number of 300 yard lengths from 1 lb  
Woollen  American run  number of 100 yard lengths from 1 oz  
Woollen  Run  number of 1,600 yards lengths from 1 lb  
Woollen  Dewsbury  number of yards from 1 oz  = number of 16 yard lengths from 1 lb  
Woollen  Galashiels  number of 300 yard cuts from 24 oz  
Woollen  Hawick  number of 300 yard cuts from 26 oz  
Woollen  Irish  number of yards from 1/4 oz  
Woollen  West of England  number of 320 yard snaps from 1 lb  
Woollen  Yorkshire  number of 256 yard lengths from 1 lb  25 drams = 1 lb, so also number of yards per dram  
Woollen  Worsted  number of 560 yard hanks from 1 lb  Worsted means combed and carded, not weight related. 
All that is required to determine the wraps per cm (w/cm) of any thread is a piece of paper about 810 cm long with two parallel lines drawn exactly 1cm apart.
I use the computer to draw the lines but careful hand drawing would work. Fold the strip ofpaper several times so that the drawn lines run across the folded paper.
Wrap the thread around the paper strip, outside of the lines, several times to anchor it then make the first wrapping on a line. Continue to wrap so that the
wrapped threads lie parallel, just touching each other but not overlapping and with no gaps. Count the number of wraps needed to completely fill the space between
the two lines. Repeat the exercise as many times as necessary to be sure that you have counted correctly.
If you need to know the thickness of the thread for lacemaking purposes refer to the charts on this page.
To measure the Tex of a yarn (the resultant plied yarn rather than of a single ply) you will need a balance or scales capable of weighing accurately in milligrams. Usually
sold as jeweller's scales one of these costs about £20. Ordinary kitchen scales are not accurate enough.
To determine the Tex of any thread carefully measure 10 metres of it and cut from the reel. Now weigh it.
Tex = weight in grams of 1,000 metres of thread, so multiply the weight of your 10 metres by 100. That figure is the Tex of the yarn.
In her book Contemporary Lace for You Jane Atkinson has recorded the Tex along with a lot of other useful notes about a wide range of threads
suitable for lacemaking. The tables of her findings are available on her website along with a lot of other observations about the threads, although I
suspect that most of theTex sizes stated are those quoted by the manufacturers rather than her own findings.