Sett Calculations and Online Resources

Updated: Jun 3

Sett is the measurement of yarn density per inch.

Once calculated, the sett number is also known as Ends per Inch or EPI

Sett is a big topic for weavers. Recently, I have been collecting information from authors who describe methods for arriving at Sett calculations and thought I would share my findings here.

Madelyn van der Hoogt recommends the Master Yarn Chart as an excellent document to find sett numbers for different types of yarn. It was developed at Handwoven Magazine under her editorship and has proved a significant boon. The chart is encyclopedic in nature with sett calculations for all the yarns ever used at Handwoven magazine. For each yarn there is a photo image, the yards per pound and a range of three sett numbers representing: Lace / Plain Weave / Twill. All sett calculations are dependent on the planned outcome, for example: lacey shawls, fancy table runners, or durable rugs.

From the Master Yarn chart:

8/2 Pearl Cotton

4200 yds/lb.

20, 24. 28

The three numbers in the bottom row show a range for assigning sett. The middle number – 24 indicates a sett for plain weave, while more open lace is sett at 20, and a tighter Twill is sett at 28. While the chart numbers are a good starting point sampling is always recommended. Yarn differences will impact the sett.

To download the Master Yarn Chart: and

Ashenhurst’s Rule / Formula

Peggy Osterkamp (among countless others) recommend Ashenhurst’s Rule for calculating sett. T. R. Ashenhurst, through his work in the cloth industry during the 19th century, created and presented a theory that could be used on power looms for a variety of thread types and has been used ever since on handlooms. Ashenhurst originally presented his “Diameter Intersection Theory” in – Textile Calculations and Structure of Fabrics, published 1884, recent reprint 2020.

Ashenhurst’s formula

Sett or Number of diameters per inch = .9 times the square root of the yards per pound.

How to calculate: Excel, hand-calculators, or other device apps will calculate the square root. The yards/lb. numbers can be found on the Master Yarn Chart.

Ashenhurst’s formula serves to establish the maximum sett for any given thread type. Again, it is a starting point. The maximum sett assumes a balanced plain weave with a 1:1 ratio of warp thread and weft thread. Weavers then do the additional multiplication to find the sett according to their purpose for the weave.

Sett = .9 times (the square root of yds//lb.) times .5 (for delicate fabrics)

Peggy Osterkamp explains further:

“Here are the percentages of the maximum sett for some types of cloth. You can go higher or lower as you determine what your yarn or purpose requires.

  • 90% for upholstery

  • 80% for “production” weaving

  • 60-70% for clothing

  • 65% for woolens

  • 50-60% for delicate fabrics, e.g., shawls

Again, the reason for wanting to know a maximum sett is so that you can take percentages of it to allow for different yarns and types of fabrics. These numbers are used for balanced setts, where the warp and weft show equally. Open up the sett (so that the wefts can pack down between the widely spaced warps) for more weft predominance, and make it closer (more warps per inch) for more warp predominance.”

The Ashenhurst Maximum Sett calculator is found online at:

Determining sett through wrapping

Photo image by Peggy Osterkamp

Wrapping is a commonly used method described by most weaving teachers and many weaving authors as a reliable way to begin determining sett. Wrapping consists of winding the warp thread around a ruler (or sett tool) for an inch. Counting threads gives the Wraps Per Inch or WPI. However, sett must include interlacement and yarn choice to be a complete calculation.

Plain weave: WPI divided by 2 (to accommodate the interlacement) = sett

Lacey structures: WPI is highly dependent on the yarn

Twill: WPI divided by 2/3 (to accommodate the interlacement) = sett

For example, Eva Stossel described a sett of 30 for pearl cotton 20/2 Huck Lace curtains, by comparison, she used the same structure for a shawl of 64/2 merino silk at a sett of 45.

Other types of calculators and online tools

Janet Dawson, weaver, educator, and blogger writes about using online calculators. She advocates for the now articulated process of using the Ashenhurst formula and the Master Yarn Chart to find a particular thread sett. However, she takes the process further, integrating the sett into a new calculator that averages sett from different types of warp threads. This averaging system can be very useful for the designer who wants to find the sett when combining diverse threads.

Her website is full of other types weaving tool calculators that make life easier, including a project calculator, and a denting calculator with associated sley order.