Weaving Reed Substitution Calculator
Enter the sett named in the draft, the reed you have, and the width you plan to sley. The calculator returns an evenly distributed denting repeat and extends it to the exact number of warp ends in the project.
Even denting repeat1-2-2
- Warp ends required
- 400
- Project denting plan
- 80 complete repeats of 1-2-2.
- Reed dents used
- 240
- Actual width in reed (in)
- 20
- Achieved sett per inch
- 20
- Sett error
- 0%
- Maximum ends in one dent
- 2
- Reed suitability
- Pass: the repeat stays at or below 3 ends per dent.
Project denting plan
| Segment | Denting | Warp ends | Reed dents |
|---|---|---|---|
| Complete repeats | 80 x 1-2-2 | 400 | 240 |
| Final partial repeat | None | 0 | 0 |
| Total plan | 80 complete repeats of 1-2-2. | 400 | 240 |
Zeroes in a repeat are empty dents.
The actual width can differ slightly because the plan must use whole warp ends and whole reed dents.
How to use this calculator
- Choose whether your sett and reed numbers are per inch or per 10 centimeters.
- Enter the target sett from the draft and the density stamped on the reed.
- Enter the planned width in the reed before weaving, not the finished width.
- Set the most ends you are willing to place in one dent for this yarn.
- Use the repeat and final partial repeat when you sley the warp.
How the reed substitution is calculated
A reed substitution asks how many warp ends should go through each dent when the reed on the loom does not match the sett named in the draft. This calculator keeps the sett and reed in the same basis, either per inch or per 10 centimeters, and distributes the heavier dents through the repeat instead of placing all of them together.
Let S be the target sett, R be the reed density, W be the planned width, and L be the basis length: 1 inch for imperial inputs or 10 centimeters for metric inputs. The required number of warp ends is:
N = round(S x W / L)
The sett and reed are converted to same-scale integers and reduced by their greatest common divisor. That gives A ends across B dents. For dent number i in the repeat, the dent load is:
p_i = floor(i x A / B) - floor((i - 1) x A / B)
The repeat therefore contains exactly A ends in B dents, while its average load is S / R ends per dent. When the target sett is lower than the reed density, some entries can be zero; those are empty dents. When the target sett is higher, the entries can be two, three, or more ends per dent.
How the project plan is built
The calculator applies as many complete repeats as will fit in the rounded warp end count. If ends remain, it appends the shortest prefix of the repeat that reaches the remaining count, trimming only the final dent when necessary. The total dents used are the complete-repeat dents plus the final partial-repeat dents.
Actual width is based on whole dents used:
actual width = dents used x L / R
Achieved sett is:
achieved sett = N / (actual width / L)
Sett error is 100 x (achieved sett - S) / S. A small error can appear when the planned width does not contain a whole number of repeat cycles, because the edge must stop on a whole dent with a whole number of ends.
What moves the result most
The ratio between target sett and reed density controls the repeat. A 20 EPI sett in a 12-dent reed reduces to 5 ends across 3 dents, so the repeat uses a mix of one- and two-end dents. A sett lower than the reed density creates empty dents, while a sett several times denser than the reed can require several ends in every dent.
What this calculator leaves out
The calculation determines thread distribution only. It does not prove that a yarn will pass through the reed without abrasion, that crowded dents will beat evenly, or that the finished cloth will have the hand you want. Floating selvedges, doubled edge ends, and separately weighted ends should be added from the draft instead of hidden inside the width.
Worked example
Suppose a draft calls for 20 ends per inch, but the available reed is 12 dents per inch and the warp is 20 inches wide in the reed. The project needs round(20 x 20), or 400 warp ends.
The ratio 20 to 12 reduces to 5 ends across 3 dents. The even repeat is 1-2-2, so 80 complete repeats use all 400 ends in 240 reed dents. The actual width is 240 / 12, or 20 inches, and the achieved sett is exactly 20 EPI with 0% sett error. The heaviest dent carries two ends, so a three-end limit passes.
Common questions
How do I use a different reed from the one named in a weaving pattern?
Enter the pattern sett as the target sett and the reed you actually have as the reed density. The repeat tells you how many ends to put in each dent. Follow the complete repeats first, then use the final partial repeat only if the project width does not stop at the end of a repeat.
What do numbers such as 1-2-2 mean on a reed substitution chart?
Each number is the count of warp ends placed in the next reed dent. A 1-2-2 repeat means one end in the first dent, two ends in the second dent, and two ends in the third dent, then the same sequence repeats.
Can a 12-dent reed produce 20 ends per inch?
Yes. Twenty ends per inch in a 12-dent reed averages 20 divided by 12, or 1.667 ends per dent. The reduced repeat is 5 ends across 3 dents, which this calculator writes as 1-2-2.
Can a reed be sleyed with empty dents?
Yes, when the desired sett is lower than the reed density. Empty dents are shown as zeroes in the repeat. Whether they are visually acceptable depends on the yarn, weave structure, finishing, and how evenly the empty dents are distributed.
How many ends can safely go through one dent?
There is no universal safe number because yarn size, hairiness, twist, reed condition, and weave structure all matter. Use the limit field as your own practical cutoff. If the result exceeds it, a denser reed or a lower sett is usually a better starting point.
Why is the actual width slightly different from the requested width?
The calculator rounds the warp to a whole number of ends and then assigns those ends to whole reed dents. If the project stops partway through a repeat, the edge dent can shift the actual width slightly. The sett error row shows the size and direction of that difference.