Information provided by Marcy Petrini
In planning a project, start with the final, or desired, dimensions, meaning the width and the length the fabric should be when ready for use. For an item like a table runner, measure the table on which the runner will be placed; if you are having trouble visualizing what the runner will look like on the table, take paper or cloth and do a mock. For items like towels, which are available in different dimensions, use a favorite towel and measure. For garments, use the manufacturer's recommendations for fabric needed, or use the pattern pieces and rethink the layout, minimizing fabric wasted. Finally, for gifts, use tables like the one enclosed as a starting point.
|Shawls||36" (beginning width) or 20"||At least 2 1/2 yards|
|Baby blankets||36" or 45" (beginning width)||2 yards|
|Afghans||60" (sew two lengths or double weave)||At least 2 1/2 yards|
|Table runners||12"- 14"||Length of the table (or 36" to 48")|
|Scarf||10" - 12"||4 feet|
|Sash||3" - 4"||1 1/2" yards|
|Napkin||17" - 18"||17" - 18" (square)|
Once the final weaving width has been decided, the width on the loom has to be calculated. This must include take-up and shrinkage.
When the warp threads are on the loom ready to be woven, they are lined up to a certain width. During weaving, the weft goes over and under them and draws them closer together. This is the take-up.
Shrinkage is caused by the process that the fabric undergoes after it comes off the loom. It depends on the fiber (See SS&D Winter 1999/2000, 21-24 for a discussion of fibers), but also on the finishing method. Hand washing in cool water will usually result in less shrinkage than washing with agitation in hot water. Finishing is good for the fabric: the yarns blossom, the fiber characteristics become alive, and the hand of the cloth improves a great deal.
The only sure way to know what the take-up and shrinkage will be is to sample and measure. Both these factors depend on the fiber, structure, sett and weaver, which are also inter-related. In sampling, a width of at least 10" should be used, because narrower widths promote a tighter beat. For these reasons, sampling nearly doubles the work of the project. More experience weavers can often estimate take-up and shrinkage. An excellent way to acquire experience is not only to weave a lot, but also to keep careful notes of the weaving. For every project, fill out a project sheet, carefully measure and record the cloth off the loom, and then again after finishing. Calculate percentages as shown in the table below. At a later date, the project sheets can become invaluable in determining take-up and shrinkage for a given yarn or structure.
Calculations of Take-Up and Shrinkage
|On the loom||15"||130" (no loom waste)|
|Off the loom||13.5"||120"|
If unknown, assume 10% of the final width for take-up and another 10% for shrinkage.
The width on the loom will be the final width, plus the take-up and plus the shrinkage. See sample calculations below.
The number of warp ends that must be wound for the project are the width on the loom multiplied by the sett (See SS&D Spring 2000, pages 45-48 for a discussion of sett). This number may have to be adjusted for the weaving structure, to have a complete repeat. For example, if using the threading of a pointed twill (1, 2, 3, 4, 3, 2, repeat), the final number of warp threads should be divisible by 6, so the repeat won't end in the middle, and an additional thread added to balance the last repeat with a thread on shaft 1.
Warp Ends Calculation: Example
|Final planned width (")||12"|
|+ Take-up (10%)||+ 1.2"|
|+ Shrinkage (10%)||+ 1.2"|
|= Width on the Loom||= 14.4" round up to 15"|
|x epi (ends per inch)||x 15|
|= Warp Ends||= 225 ends|
|+/- Adjustment for pattern||-2 (adjust for twill, add balance thread)|
|= Total Ends to Wind||= 223|
Next, we turn our attention to the length of the project. For this step, it's best to plan the length of each item, and then multiply the calculated length by the number of items to be woven. That is, plan the length to be woven for each towel, and then multiply by the number of towels to be woven. See sample calculations below.
A hem or other treatment must be applied to the raw edges of the weaving. The selvedge edges are finished, if enough attention is paid during weaving; the beginning and the end of the fabric will require to be finished so that the weaving won't unravel or become unstable. To the final length of each piece, add the length of the hem, if there is to be one; 1" on each side is a good place to start.
Next we add shrinkage. The same considerations apply for the length as do for the width, and the 10% figure can be used if this is not known more accurately.
The final length, including hems, plus the shrinkage is the width of each item to be woven. This measurement should be made on the loom, with the tension off.
If the item is to have a fringe, that length is added at this point. If only one item is to be woven, no additional length may be needed, as the warp waste (discussed below) can be used for this purpose. But when more than one item is woven, each will need a fringe on both sides. This amount should be added to the length to be woven.
Take-up is added to this length. Before being woven, the warp is straight on the loom. When the weft is inserted, the warp threads are no longer straight in the cloth, but follow a path that goes over and under the weft. Thus, a warp thread that started 10" long on the loom may become 9" of fabric once woven. This 10% loss is the take-up. Use this 10% figure if a more exact measure is not known.
To sum of the length to weave, the fringe, if any, and the take-up is the length of warp that must be allowed per item. Multiplying this length by the number of items gives the length of the warp needed to weave all the items.
The final step in calculating the length of the warp to be wound is to add the loom waste. The warp will be tied-up at the front beam; that part won't be woven, and is part of the waste. The other part of the waste occurs at the end; the warp will be advanced until either the rod will be at the back of the shafts and cannot be advanced any further, or it is impossible to obtain a clean shed, and thus weaving cannot continue. This left over warp is also part of the loom waste. Both the front and the back loom waste can be used for fringes, if the item calls for them.
Loom waste depends on the loom, the weaving structure and how well tensioned and wound on the warp is; 18" is a common need, but use 24" if unsure. Being short of warp at the end of the project is very disappointing. Measure loom waste regularly, to determine what should be used for a given loom.
Warp Length Calculations
|Final length, include hem (")||54" (2" hem)|
|+ Shrinkage (10%)||5.4"|
|= Length To Weave (")||59.4", round up to 60"|
|+ Fringe (")||0"|
|+ Take-up (10%)||5.4"|
|= Length per article (")||65" (round off)|
|x number of articles||2|
|= Warp length for weaving (")||130"|
|+ Loom waste (18" or 24")||24"|
|= Total warp length (")||154"|
|= Length of each warp thread (/36 to convert)||4.3 yards|
The length of each warp thread multiplied by the number of warp threads is the total amount of yarn needed for the project warp.
Amount of Yarn Needed for Warp
|Total Ends To Wind||223|
|x Length of each warp thread (yards)||x 4.3 yards|
|= Total warp needed (yards)||= 960 yards|
Next the amount of weft needed for the project must be calculated. If the weft is the same size as the warp, the warp amount can be doubled safely. Actually, less weft than warp is needed to weave the project, since the loom waste is not woven. However, as there is always some inaccuracy in the amount of yarn purchased by weight (as described below), and some waste if knots are encountered in the yarn, buying double the warp is a safe assumption. For a very expansive yarn, or if the weft is of different size as the warp, the weft amount must be calculated.
To calculate the weft amount, multiply the width of warp on the loom by the beat (shots per inch) and by the warp length for weaving.
Amount of Yarn Needed for Weft
|Width on the Loom (")||15"|
|x Beat (shots/inch)||x 15 shots/inch|
|x Warp length for weaving (")||x 130"|
|= Total weft needed (")||= 29,250"|
|= Total weft needed in yards (/36)||= 813 yards|
The amount of yarn to buy is the amount needed for warp plus the amount needed for weft. In the example shown, 1,773 yards (960+813). However, yarn is usually purchased by weight, so the 1,773 yards must be converted to ounces or lbs. Conversion factors are usually available from the manufacturer, or in tables (See SS&D, Summer 93, 54-57, for example).
For this example, a twill sett at 15 ends per inch could use 3/2 cotton, which has 1,200 yards to the lb. To convert, divide the yards needed by the conversion factor.
Converting from Yardage to Weight
|/ Conversion factor for 3/2 cotton (yards/lb.)||1,200 yards / lb.|
|Weight of yarn needed (lbs.)||1.48 lbs.|
In some cases it may be possible to purchase 1½ lbs. of yarn; in other cases, the yarn amount has to be rounded up to the next available quantity. Here, 2 lbs. may have to be purchased.
Of course, if the warp will be a different color than the weft, each one is calculated individually. In this example, 960 yards / 1,200 yards / lbs. = 0.8 lbs of warp or approximately 13 oz. For weft, 813 yards / 1,200 yards / lbs. = 0.7 lbs. or approximately 11 oz. If the yarn is not available by the ounce, a lb. of each must be purchased. In general, though, it is safest to buy a slightly larger amount anyway, just to be safe, since the 1,200 yards per lb. is an average and there is a range. Furthermore, it's easy to be off. For example, winding a warp only 1 extra inch, an increase that is hardly noticeable, results in needing 223 extra inches, or 6 extra yards of thread. Similarly, if the beat is slightly off, 15.5 shots to the inch, rather than 15, an extra 27 yards of weft are needed.
If different colors are going to be used, for example in stripes or plaids, each color amount could be calculated individually using the methods just described, assuming each color to be its own warp and weft, or a percentage can be estimated. For example, in the above example, if out of the 15" of warp, 5" are to be dark blue, the rest light blue, approximately 1/3 of the warp, or 5 oz of dark blue are needed, and 2/3 of the warp, or 9 oz. of the light blue are needed.
Careful calculations do take a bit of time, but in the long run they save time, money and frustration, and can give the weaver valuable experience that can be used over and over again.