I thought some information for how to calculate yardage for different types
of yarn might be helpful. Each fiber-type of yarn has its own "system" for
measuring its yardage. (Some fibers have several systems, such as all the
different woollen counts of English yarns). Many manufacturers and suppliers
are switching over to the metric system count for natural fiber yarns, but
you will still run into the old counts, too.
 
COTTON    magic number = 840
 
Take the size and ply of the cotton and reduce it to a single number. A size
10/2 cotton refers to a size 10 cotton, 2 ply. Thus a 10/2 cotton = 5, an
8/4 = 2, a 15/2 = 7.5. Multiply this number by 840 and this  = yds/lb.
 
 
LINEN    magic number = 300
 
Take the size (called the "lea") of the linen, if a fraction, reduce to a
single number. A size 3 lea linen means no ply, 3 x 300 = 900 yds/lb. A 5/2
means a 5 lea linen, 2 ply. 5/2 reduces to 2.5. Multiply this times 300 =
yards/lb.
 
 
WORSTED WOOLS (combed wools)    magic number = 560
 
Same rules apply. Multiply the reduced number by 560 = yds/lb
 
 
WOOLEN SPUN YARNS    magic number = 1200
 
1200 is the most used in the USA. England uses many different local
numbering systems, often named after the town or area using that number (as
in "Bradford count" or "Galashiels count"). Same procedure as above,
multiply the reduced number by 1200 = yds/lb
 
 
METRIC SIZES -- apply to all yarns using this method, not fiber specific
                magic number = 1000 meters/kilo (or almost exactly)
                               500 yds/lb
 
These are the easiest to use. The metric system is used in Europe to apply
to all fiber types. The number of the yarn refers to the metric size/number
of plys. Thus a 10/3 = a size 10 metric, 3 ply. You reduce the number as
above. So a 10/3 reduces to 3.3 x 1000 = 3330 meters/kilo (2.2 lbs)
  or  3.3 x 500 = 1665 yds/lb.
 
 
Spun Rayon yarns use the cotton system.  Blends usually use whichever fiber
predominates in the blend. Thus a 65% cotton/35% acrylic blend would be
measured on the cotton system. A similar blend of wool/acrylic would be
measured on the wool system.
 
Synthetics can be filament yarns and measured on the denier system.
You will not run into these often in art/craft yarns so they are not
discussed here.
 
----------------
 
Susan