Weaving Calculations — Plain Weave on a Rigid Heddle Loom

Weaving calculations — a PITA or a necessary evil?  Fear not, my young Padawan, for I will do my best to show you a methodical way of keeping your project & mind (mostly) organized so that you can fly through the calculations quickly & accurately and onto the fun stuff–weaving!

Since many new weavers start out on a non-harness loom, such as a rigid heddle loom, I will focus today’s math drama on Plain Weave aka Tabby aka Balanced Plain Weave.   This post may seem long, but I am attempting to share my thought-process on how I would tackle this project, so think of it as WWKD (what would kibbles do?).

• Pick a project.  Well, duh!   But in all seriousness, I get PMs from warriors who are freaked out about the weaving calculations, but they can’t tell me what they are planning to weave.  Seriously, once a project is picked, then we can proceed.  WWKD: well, I have a 25″ Schacht “Flip” rigid heddle loom and weaving on a rigid heddle is not my strong suit, so I think I will weave a small project:  a piece of cloth 11″ wide by two yards long.
• Decide on sett or epi (ends per inch) which determines the density of your fabric. Want more drape, use less warps ends per inch…want a denser fabric, add more ends per inch.  If you buy weaving yarn (usually comes in a cone), the manufacturer will have the sett for their product on the inside of the cone or on a tag.  If you want to use knitting yarn or an unknown yarn (both of which are completely fine to do!) you will have to measure the sett yourself.  Easy peasy.

To the left, you can see I’ve wrapped some sock yarn around a ruler for an inch.  I have 16 wraps here that are side-by-side, do not overlap, and not pulled too tightly.  Since my project is Plain Weave, I will take my number of wraps per inch and divide it by two: 16/2 = 8 epi (ends per inch).  This is my sett for Plain Weave.  WRITE THIS DOWN!   You can find sett charts for the most common fibers in many weaving books & by Googling it.  Be warned that many of them will list fibers with sizes as 8/2 or 10/2 instead of using terms such as worsted weight or sport weight.   WWKD:  I always use a ruler to determine WPI and I keep detailed weaving notes so that I can compare fabrics to see what works and what doesn’t.   Experience is your best guide here and that comes with Practice, Practice, Practice!  

• Deciding which rigid heddle size to use:   There are many dent sizes of rigid heddles to choose from; however, you may have only one or two available…that’s ok, too.  The dent size of a rigid heddle (and also reeds for harness looms) is related to epi (ends per inch).   I frequently use a 12-dent reed, which means for every inch in my reed, there are 12 threads going through the reed.  This will also be true for rigid heddles.
  • Recall our sett/epi calculations above:  We had 16 WPI and divided this by two to get a sett number of eight epi.  As it turns out, there is a rigid heddle/reed size of eight.  This is perfect for us in our plain weave example.  Yay!
  • Don’t have a size eight heddle?  No problem!   If you have a size 10 rigid heddle, you can still weave with the above sock yarn, but your final cloth will be a bit more dense than if you had used a size eight.  Why?  There are two more threads per inch in your cloth than one using a size eight.  Use a size 12, your fabric will be denser still with four more threads per inch.
  • If you use a size FIVE heddle, well…you could still weave that sock yarn with that size heddle, but your final fabric will be quite loose and “holey” or “open weave” as shown on the right.   If that’s the look you’re after, then use a size FIVE heddle with that sock yarn, warrior!

• Calculating Warp:  I already decided my project was going to be two yards long (e.g. 72″ long because a yard is 36″ long & I want two yards); however, if I warp my loom with only two yards of yarn, I will be sorely disappointed in my much too short cloth!                                                             When calculating, use all inches or all centimeters–Don’t mix your units or you’ll be sorry!!  Seriously, peeps!  Yards + inches + centimeters = waste of time & money!!

Length of project desired + any fringe + loom waste + shrinkage

72″ + 0″ + 10″= 82″   — the first three of the above list

For shrinkage, standard percentage is about 10%, so 10% of 82″ is 8.2″ (i.e. 82 x 0.1 = 8.2).    Now add this to the above:  82″ + 8.2″ = 90.2″

• Calculate number of warp ends:  Look for that piece of paper where you wrote down your epi — it was 1/2 the number of wraps around a ruler for an inch.  In our case, that number is eight.   In the beginning, I had decided I wanted a cloth that was 11″ wide.  As we weave, there is a natural draw-in that occurs, so add ~10% to the width you want and calculated width is now 12″ (11″ + 1.1″ = 12.1″ but rounded down to 12″). We take this number and multiply this by our epi:

ends per inch (epi) x width desired = number of warp ends

8 x 12 = 96 warp ends

What does this tell you?

• If you are using a warping board/mill, then you will wind 96 2.5-yard rounds (because 90.2″ divided by 36″ (the number of inches in a yard) is approximately 2.5 yards).
• If you are direct warping, 48 ends will go into slots and 48 will go into holes (96 ends divided by two (i.e. slots & holes) =48)

• Calculating TOTAL YARDAGE of WARP:  We already know that we need ~90″ for each warp end (~2.5 yards for each end) AND we know we will use 96 warp ends.  Multiple these two numbers together:

Length of each warp end in YARDS x Number of warp ends= TOTAL yards of warp

2.5 yards x 96 warp ends = 240 yards

Why do we want this number?  When we purchase yarn, it is generally sold in skeins by weight & yardage.   You don’t want to run out of yarn, do you?  No, Precious, you don’t!

• Calculating Weft:  Yes, you still have more calculations to do, but don’t fret!  Since we are going to weave Tabby (Plain weave) and are going to do it balanced (i.e. same number of warp ends per inch as weft, aka picks per inch) -or- you don’t care that it’s balanced or not, you just want to weave, then all you need to do for either of these situations is to look at what you calculated for warp.  

Total warp yardage = Total weft yardage

240 yards = 240 yards

• Therefore, Total yardage for this entire project is then….drum roll…

240 yards + 240 yards = 480 yards!!!

Naturally, if you’re going to put in colored stripes in either warp and/or weft, you can do further calculations (or not!) depending on how wide or narrow you wish your stripes to be.  If you put stripes in both warp & weft, you’ll get squares/rectangles.  :) If you’re using expensive yarns or don’t wish to have a lot of left over yarns, doing these further calculations will be necessary for you.  If you don’t care about spending extra money on yarn or want extra oddments for other projects, then at least you have an idea of how much total yardage you need for your project.

Plain weave draft and optional drawdown.

• Plain weave draft & drawdown:  It’s pretty simple and feel free to use this one in your next plain weave dissertation.  :)

• N.B.–Please note that these calculations are geared toward PLAIN weaving.  If you’re going to weave twill, your sett and other calculations WILL be different.   I will have future weaving posts that will focus on other aspects of weaving.  Be on the look-out!  :D

• If you have any questions regarding weaving, weaving drafts, or weaving calculations for your next dissertation, please don’t hesitate to contact me!!   I <3 weaving!!!