Warp math has four ingredients: the woven length, take-up and shrinkage, loom waste, and your sett: the ends per inch, set by your reed. Enter them once and you get the warp length per end, the ends to wind, and the warp and weft yardage to buy.
Your Project and Loom
Wind Your Warp
160ends
each 108 in (3.00 yd) long
Wind 160 ends at 108 in on the warping board.65 in woven + 7 in take-up + 36 in loom waste.
- Warp length per end108 in
- Warp yarn480 yd
- Weft yarn318 yd
- Total798 yd
The Formulas
warp length per end = woven length + take-up % + loom waste · ends = width × settwarp yards = ends × length per end ÷ 36 · weft yards = width × picks per inch × woven length × 1.10 ÷ 36Take-up is the length the warp loses bending over and under the weft; loom waste is the warp your loom keeps: tie-on at both ends and the stretch that never reaches the fell. Weft takes its own 10% for the same bending.
Worked Example
An 8 in wide scarf, 65 in woven length (63 finished plus hems), sett 20, 20 picks per inch, 10% take-up, 36 in loom waste. Handwoven’s own example:
- Length per end: 65 + 6.5 + 36 ≈ 108 in = 3 yd.
- Ends: 8 × 20 = 160. Warp: 160 × 3 = 480 yd.
- Weft: 8 × 20 × 65 = 10,400 in, plus 10% → 11,440 ÷ 36 = 318 yd.
Common Setts for Plain Weave
Half the WPI is the plain-weave rule; twills sett closer. Your yarn’s wraps per inch set the row.
| Yarn (by WPI) | Plain weave sett | Twill sett |
|---|---|---|
| 30 WPI (lace) | 15 epi | 20 epi |
| 24 WPI (fingering) | 12 epi | 16 epi |
| 16 WPI (sport–DK) | 8 epi | 10–12 epi |
| 12 WPI (worsted) | 6 epi | 8 epi |
| 8 WPI (bulky) | 4 epi | 5–6 epi |
How to Find Your Inputs
- Sett: wrap the yarn on a ruler for WPI and halve it for plain weave, or follow the pattern. Balanced weave means picks per inch ≈ sett.
- Loom waste: measure a finished warp’s thrums once, apron-rod tie-on at both ends plus unweavable stretch, and keep that number for your loom forever.
- Woven length: finished length plus hems or fringe, before take-up. Fringe twists out of the loom waste on many projects: don’t pay for it twice.
Assumptions and Defaults
- Take-up and shrinkage ride together as one percentage on the warp; wet-finishing heavy shrinkers (woolens) deserves 15% or more.
- Weft carries a fixed 10% take-up.
- No draw-in allowance on ends; add 2–4 floating selvedge or edge ends if you weave with them.
- Yardages round up to whole yards.
Warp Questions, Answered
How do I calculate warp length?
To calculate warp length, add the woven length, the take-up (about 10% for plain weave in spun yarns), and your loom’s waste, which covers the tie-on at both ends and the length behind the heddles. The scarf example comes to 108 inches per end from a 65 inch woven length.
How many warp ends do I need?
The number of warp ends you need is the width on the loom times the sett, so 8 in at 20 ends per inch is 160 ends. If you weave with floating selvedges, wind two more ends, one for each edge, so the selvedges catch the weft cleanly.
What sett should I use for my yarn?
A good starting sett for your yarn is half its wraps per inch for plain weave, so a 24 WPI yarn setts at about 12. Twills set closer and lace more openly, and when the yarn is precious, weave a sample first, because a sett one end off can make cloth that is too stiff or too loose.
How much loom waste should I plan for?
Floor looms commonly waste 24 to 36 inches of warp, and rigid heddle looms 18 to 24 inches. That waste applies per warp rather than per item, which is why weavers often put several projects on one long warp and share the waste across them.
Do warp and weft take the same amount of yarn?
Warp and weft don’t take the same amount of yarn, since in balanced plain weave the weft runs lighter because it has no loom waste. The scarf example takes 480 warp yards and 318 weft yards, and using different fibers in each is common practice: a strong, smooth warp with a soft, lofty weft.