Determining sett by getting the diameters on a ruler is easy to do with a heavy yarn, but it would be terribly hard with a slippery, or nubbly, or fine thread. There’s a way to find the diameters using a pencil, paper and an inexpensive calculator. For me, this makes finding the sett a piece of cakeÑno hassle or worry that the threads are touching too much or not enough. This method of calculating the diameters was worked out by Mr. Ashenhurst long ago for industry.This calculation will give you the number of diameters which will determine the maximum sett for a fabric. The reason you want to know the Ashenhurst number (the maximum sett) is that it’s his number that is used to make allowances for yarns, weave, shrinkage, finishing, purpose (e.g. upholstery or sheer curtains, etc.).Using Ashenhurst’s formula, you will find that the number of diameters will be more than if you wrapped the yarn on a ruler. I think the reason his number for diameters is higher is that it’s a mathematical formula which he found to work. The two methods (Ashenhurst and wrapping) can be compared. You can use whichever method seems convenient to you. Surely, you would use Ashenhurst for a warp of sewing thread. It’s likely that you would use the wrapping method for a large wool yarn. But, remember, you will get different numbers if you compare both methods on the same size thread. If you wrapped a yarn and counted the diameters, and you took 1/2 of that number for plain weave, you would need to divide that number by 0.7 to get a number close to Ashenhurst’s.An example might be a yarn wrapped 10 times on a ruler (=10 diameters/inch). Half of that is 5, for plain weave. Divide 5 by .7 to get a number that about equals Ashenhurst’s maximum sett for plain weave.5 divided by .7 = 7
The maximum sett would be 7, not 5. Before I give you Ashenhurst’s formula, you need to understand that you’ll have to push a special key on your inexpensive calculator. It’s the square root key and looks a lot like a check. See Figure.
To find the square root of a number, enter the number on your calculator then push the square root key. 
Now for the formula:Number of diameters per inch = .9 times the square root of the yards per pound
That’s it!! That gives you the number of diameters of the yarn in an inch (the calculated number). (On the calculator enter in the yards per pound, then push the square root key. Multiply that number by .9). For example, take a yarn that has 1,000 yds per pound.

The reason I like this method is that it’s so fast and reliable–no worrying whether the yarns are wrapped properly on the ruler.It’s as simple as pushing a few keys on the calculator. Remember, I said you could compare the two methods–wrapping and Ashenhurst. To make the wrapping method equal to the Ashenhurst, divide the wrapping sett by .7. That will increase the number arrived at by wrapping, so it will give you the Ashenhurst maximum sett. 
Read more in Weaving for Beginners and Book #1: Winding a Warp & Using a Paddle
Your verbal description says to find the square root and then multiply by .9. The example shows multipling by .9 2 times. The sample seems to come up with the “right” answer.
Don’t know about a verbal description but I think the tip is correct as per this:
Square root of 1000 is 31.62
Times 0.9 is 28 that’s the diameters of the yarn
For plain weave times 1/2
ORFor twill times 2/3 (0.67)
Now you have the maximum sett
Next take the percent of the max for your purpose
I usually take 80% for for regular cloth
(For upholstery you would take 90%
In my books for beginners and book #1 i have this all worked out in charts
Hope this helps
Peggy
Thank you Peggy! This is so handy. Wrapping has never been my favorite thing.
Could you comment on what percentage you’d use for warpfaced plain weave, starting from the Ashenhurst number?
My teachers told us to double the sett for really warp faced things. I would take it from there–maybe double the 80%–can’t give a definite answer.
Hi Peggy.
Do you know if what you say – take the percent of the max for your purpose – is the same as the K factor?
I love your blog! It’s so helpful to refresh my memory as I’ve just taken up weaving again after a 25 year gap. Thank you!
No, I don’t know the answer.
Hi Peggy,
Love the blog and got the book, however most of my yarns come in meters per kilo these days. Does Ashenhurst still work? If not, what adjustments do I need to make?
English weaver
Yes, Ashenhurst works for the metric system. You just have to convert the meters to yards and the kilos (kg) to pounds then you have yards per pound.I show how to do this on page 273 in my Weaving for Beginners book. Read on. However, in the 14 pages of Sett Charts in the back of my Book #1: Winding a Warp & Using a Paddle, there are columns for both: yd/lb AND m/kg. There is a onepage chart in my Weaving for Beginners book on page 381. So all you have to do is look up your meters per kg in the charts and all is worked out for you.
NOW here’s how you can do it yourself. Convert meters to yards using the worksheet on page 273: take meters X 1.09 = yards. Inside the back cover are Useful Equivalents you see that 1 kg is equal to 2.2 pounds. So far you know that you you have the yards in 2.2 pounds (your yards you calculated are for 1 kg. and 1 kg. equals 2.2 pounds). So take your number and divide it by 2.2 to find out how many yards are in ONE pound. Better yet–use the charts.
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Thank you so much! This is precisely the information I have been looking for!
Is there a way to calculate for an unbalanced weave? e.g. 8/2 cotton warp with 20/2 silk weft?
Start by calculating the setts for each yarn. See if it is reasonable to use those–the one for the warp the other for the weft. It’s a good starting point. Remember to use the 80% if needed.
Peggy