What is a sett?
Once you have chosen a yarn(s) to use use for a warp you need to consider the sett. In other words, the number of warp ends you will want to have in your woven cloth per centimetre/inch (ends per centimetre (EPC) or ends per inch (EPI)).
Things that may affect the sett
There are a number of factors that need to be taken in to consideration and may affect the sett you choose:
Weave structure
A weave structure with fewer weft intersections with the warp will require a higher sett. For example a 3/1 twill will require a higher sett than a plain weave.
Final use/aesthetics of the fabric
If the final outcome is to be a lightweight scarf then the sett may need to reduced considerably. On the other hand if the fabric is to be cut and sewn a much higher sett is needed so it holds together well. A higher sett will also make it harder wearing.
Personal preference
Some weavers prefer to use a slightly higher/lower EPC/EPI and may also beat down their weft harder/more softly.
Bearing this in mind the below is only a guide and other factors will affect the sett.
How to work out the sett
To work this out you need to take your yarn and wrap it around a ruler. Do this with no gaps between but ensure the yarn does not bunch up or overlap. Wrap it around in a 1 cm or 1″ section as shown below.
Dividing the number of times the yarn was wrapped by 2 gives you the EPC/EPI of your woven cloth.
This method is usually a good indicator of the number of ends you will need for a balanced plain weave structure. When we talk about a balanced plain weave we mean a plain weave where the warp and weft are equally visible, neither one dominates the other.
For a balanced twill you would use 2/3 of the number of ends round the ruler.
In the photo above the yarn was wrapped around the ruler 14 times within 1cm. This means I would want to start with 7 EPC for a plain weave or 10 EPC for a twill.
If different structures are to be woven then the EPC/EPI will need to be adjusted. There is a formula to work this out mathematically which can be confusing. It may also be affected by previously mentioned variables which cannot be taken into consideration with a formula. The formula is as follows:
S= T X R
bn(I + R)
S is the sett.
T is the number of times the yarn was wrapped around a ruler.
R is how many ends there are in one repeat.
I is the number of weft intersections in one repeat.
I personally prefer to use the first method mentioned and adjust it taking all other aspects of the woven piece in to consideration. Sampling really is the only way to get just the right sett.