Loom Warp Calculator

Warp ends, warp length, and yarn needed from project size and sett.

What it does

Every woven project starts at the warping board or mill. The warp is the set of lengthwise threads, and getting its count and length right decides whether the project can be woven at all. Too few ends and the cloth comes out sleazy; too short a warp and the last inches cannot be finished.

Warp count is simple arithmetic. The width in the reed times the sett gives the number of ends. A 20 inch warp at 12 ends per inch needs 240 ends, and the same warp in centimeters uses ends per centimeter against the width in centimeters. Both modes land on the same thread count for the same physical cloth.

Warp length is where most beginners come up short. The finished length is only the start. Weaving pulls in the cloth, called takeup, and most looms cannot weave the last stretch near the front beam, called loom waste. Fringe is cut from the warp beyond the cloth. The total goes on the beam, not the finished length.

A common default is 10% takeup, which suits plain weave in medium yarns. Tightly set or textured cloth can take more. Loom waste runs from 18 to 36 inches depending on the loom, and fringe usually adds 6 to 10 inches per end, more for a long twisted fringe.

Once the ends and length are known, yarn yardage follows. Multiply the ends by the warp length in inches, then divide by 36 for yards. The answer tells you how much yarn to wind and whether you have enough cones. Add a little margin for broken threads and a lashing error.

For multiple pieces on one warp, add a fringe allowance for each piece and let the takeup apply to each finished length as well. Cutting the warp between pieces separates them, and the total warp length grows with the count of pieces.

How to use

1. Choose Imperial or Metric.
2. Enter the warp width as it will sit in the reed.
3. Enter the finished length of one piece.
4. Enter the sett from your reed or heddle.
5. Set takeup, loom waste, and fringe to match your loom and finishing plan.
6. Set the number of pieces if the warp makes more than one.
7. Read the ends, the total warp length, and the yarn yardage.

Formula

Ends

Total warp threads across the width.

sett

Ends per inch or per centimeter, from the reed or heddle.

takeup

Percent the cloth shortens during weaving.

waste

Length lost at the front and back of the loom.

fringe

Warp extension per piece for fringe or hem.

pieces

Number of finished items from the warp.

Takeup applies to each finished length because every piece pulls in as it is woven. Fringe applies per piece as well, while loom waste is counted once at the end of the warp. The yarn figure is total warp yardage and does not include weft, which is usually estimated separately.

Worked example

Reference table

Limits

• Assumes a rectangular warp with even sett and no floating selvedges or doubled ends.
• Takeup varies with weave structure, yarn, and tension; 10% is a starting point.
• Does not include weft yarn or the extra ends some patterns add for selvedges.
• Loom waste depends on the specific loom and how the warp is attached.

Common mistakes

• Winding the warp at the finished length and forgetting takeup and waste.
• Counting the sett from the wrong reed dent or heddle slot.
• Forgetting fringe length on a scarf or towel warp.
• Planning yarn for one piece when the warp makes several.
• Ignoring the yarn lost to threading errors and broken ends.

Try it yourself

Quick checks. Answers sit tucked under each question.

Questions

Sources

• Carnegie Mellon University: calculating yarn for a weaving project
• Portland Handweavers Guild: project planning worksheet

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