Ashenhurst's Formula

As an alternative to just wrapping yarn around a ruler, and estimating the best ends per inch for weaving a particular yarn, Ashenhurst's formula offers a more precise method of arriving at a sett. This information was provided by Donna Maurer.

To find the diameter number (D) of a yarn

For firm yarns such as worsted wool and cotton
D = 0.9 x square root (yarn count x standard yards/lb)

For soft yarns such as woollen yarns and tweed yarns
D = 0.84 x square root (yarn count x standard yards/lb)

Ashenhurst's formula gives the maximum sett of a yarn. The formula
is based on:

• number of ends of warp in one repeat of the pattern

• number of times the weft passes from one side of the fabric to the other (intersections)

• the thread diameter number (D)

• Maximum sett = D x ends per repeat/(ends + intersections)

Few cloths would be woven to this standard of firmness which gives
the maximum sett possible for a square cloth (with the same epi & ppi)
and the same yarn for warp and weft. A good working sett is about 3/4
of this number or slightly more

Example:
An 8/2 cotton has 2 plies of size 8 yarn, with a final count of 4.
It has 3360yd/lb (840yd/lb x 4).

D = 0.9 x sq rt(4 x 840)
= 52

Maximum sett (plain weave)
= 52 x 2/(2+2)
= 26

Maximum sett (2/2 twill)
= 52 x 4/(4+2)
= 34