To Change from One Count to Another Count and Find Sett or Picks to Retain the Same Character of Cloth
This rule explains how to change the yarn count while keeping the cloth character nearly the same. Here, cloth character means the general feel, firmness, cover, openness, handle, and appearance of the fabric.
If the yarn count is changed from coarse to fine, or from fine to coarse, the sett or picks cannot usually remain the same. The number of ends per inch or picks per inch must be adjusted.
Core Idea
If a finer yarn is used, more ends per inch or picks per inch are required to maintain the same cloth character.
If a coarser yarn is used, fewer ends per inch or picks per inch are required.
For example, 60s yarn is finer than 40s yarn. Therefore, if a fabric made with 40s yarn has 60 ends per inch, the same type of fabric made with 60s yarn will require more than 60 ends per inch.
Why Square Root Is Used
Yarn count does not change linearly with yarn diameter. In the cotton count system, yarn diameter is approximately proportional to the reciprocal of the square root of the count.
\[ \text{Yarn diameter} \propto \frac{1}{\sqrt{\text{Count}}} \]
This means that 60s yarn is not simply 1.5 times thinner than 40s yarn. Its diameter changes according to the square root of the count ratio. Therefore, when the count changes, the sett or picks must also be adjusted according to the square root relationship.
Rule
The rule may be expressed as:
\[ \frac{\sqrt{\text{Given Count}}}{\sqrt{\text{Required Count}}} = \frac{\text{Given Sett}}{\text{Required Sett}} \]
Or, more practically:
\[ \text{Required Sett} = \text{Given Sett} \times \frac{\sqrt{\text{Required Count}}}{\sqrt{\text{Given Count}}} \]
Where:
- Given Count = original yarn count
- Required Count = new yarn count
- Given Sett = original ends per inch or picks per inch
- Required Sett = new ends per inch or picks per inch
Example
Suppose the original fabric has:
- Yarn count = 40s
- Sett = 60 ends per inch
Now, the fabric is to be made using 60s yarn. The required sett is calculated as follows:
\[ \text{Required Sett} = 60 \times \frac{\sqrt{60}}{\sqrt{40}} \]
\[ = 60 \times \sqrt{\frac{60}{40}} \]
\[ = 60 \times \sqrt{1.5} \]
\[ = 60 \times 1.225 \]
\[ = 73.5 \]
Therefore, the required sett is approximately:
\[ 73.5 \text{ ends per inch} \]
In practical weaving terms, this may be rounded to:
\[ 73 \text{ or } 74 \text{ ends per inch} \]
Meaning in Simple Textile Language
A fabric made with 40s yarn and 60 ends per inch has a certain closeness and cover. If the yarn is changed to 60s, the yarn becomes finer. If the sett remains at only 60 ends per inch, the cloth will become more open, lighter, and less covered.
To preserve the same character, the sett is increased to around 73–74 ends per inch.
So:
\[ 40s \text{ yarn at } 60 \text{ sett} \]
is approximately equivalent in character to:
\[ 60s \text{ yarn at } 73.5 \text{ sett} \]
Rule 2
Rule 2 gives the same answer in another form. It may be expressed as:
\[ \frac{\text{Given Count}}{\text{Required Count}} = \frac{\text{Given Sett}^{2}}{\text{Required Sett}^{2}} \]
Or:
\[ \text{Required Sett}^{2} = \frac{ \text{Required Count} \times \text{Given Sett}^{2} }{ \text{Given Count} } \]
Using the same example:
\[ \text{Required Sett}^{2} = \frac{60 \times 60^{2}}{40} \]
\[ = \frac{60 \times 3600}{40} \]
\[ = 5400 \]
\[ \text{Required Sett} = \sqrt{5400} \]
\[ = 73.5 \]
Therefore, both Rules give the same answer.
Applying the Same Rule to Picks
The same method applies to picks per inch.
Suppose a cloth has:
- 40s weft
- 56 picks per inch
Now suppose 60s weft is to be used. The required picks are:
\[ \text{Required Picks} = 56 \times \frac{\sqrt{60}}{\sqrt{40}} \]
\[ = 56 \times 1.225 \]
\[ = 68.6 \]
So the new picks per inch would be about:
\[ 69 \text{ picks per inch} \]
Changing from Finer Yarn to Coarser Yarn
The reverse is also true. Suppose the cloth has:
- 60s yarn
- 72 ends per inch
Now suppose 40s yarn is to be used. The required sett is:
\[ \text{Required Sett} = 72 \times \frac{\sqrt{40}}{\sqrt{60}} \]
\[ = 72 \times 0.816 \]
\[ = 58.75 \]
So the new sett would be approximately:
\[ 59 \text{ ends per inch} \]
Because 40s yarn is coarser, fewer ends are needed to give a similar cloth character.
Summary Table
| Original Yarn | Original Sett | New Yarn | New Sett Approx. | Result |
|---|---|---|---|---|
| 40s | 60 EPI | 60s | 73.5 EPI | Similar cover and firmness |
| 60s | 72 EPI | 40s | 58.8 EPI | Similar cover and firmness |
| 30s | 48 EPI | 40s | 55.4 EPI | Finer yarn needs higher sett |
| 80s | 96 EPI | 60s | 83.1 EPI | Coarser yarn needs lower sett |
Practical Interpretation
This rule is useful when a manufacturer wants to change yarn count but still produce a fabric that looks and feels similar. For instance, if 40s yarn becomes unavailable and 60s yarn is used instead, the sett or picks must be increased to compensate for the finer yarn.
Similarly, if a coarser yarn is used, the sett or picks must be reduced, otherwise the fabric may become too tight, heavy, stiff, or difficult to weave.
Important Caution
This rule gives an approximate theoretical sett. In actual weaving, the final sett may need adjustment because cloth character also depends on several practical factors, such as yarn twist, fibre quality, weave structure, reed space, crimp, loom tension, finishing shrinkage, desired cover, and whether the cloth is plain, twill, satin, drill, poplin, or another weave.
Therefore, this rule should be treated as a starting point, not as an absolute final production value.
In One Simple Sentence
When changing from one yarn count to another, adjust the sett or picks in proportion to the square root of the count ratio so that the fabric retains nearly the same appearance, cover, and character.
You can ask it in the My Textile Notes Discussion Forum.