Yarn Quantity Calculator

Draw-in and length shrinkage are different physical effects that happen at different times. Draw-in narrows the fabric while it's still on the loom, as weft tension pulls the warp threads inward during weaving, so it only affects the width you need to warp (widthOnLoom = finishedWidth / (1 − drawIn%)). Take-up and shrinkage act on length: take-up happens during weaving as warp threads bend around the weft, and shrinkage happens later during wet-finishing, so both divide the length calculation instead.

The calculator computes warpLengthInches as (finishedLength + loomWaste) divided by both the take-up and shrinkage factors. Adding loom waste before those divisions means the waste allowance itself gets slightly inflated by the same percentages, which is deliberately generous — it ensures you wind enough total thread length even though the tie-on and apron sections of loom waste never actually pass through take-up or shrinkage themselves.

Each weft pick doesn't travel in a straight line across the warp — it undulates over and under each warp thread, so it actually consumes more yarn than the flat on-loom width. The calculator accounts for this with weftPerPick = widthOnLoom × 1.1, adding a flat 10% to every pick's yarn consumption before multiplying by total picks. This is a fixed assumption baked into the formula, not adjustable through an input.

Both take-up and shrinkage are clamped between 0% and 50% in the calculator, and each division is floored at a denominator of 0.01 to prevent a divide-by-zero error at extreme inputs. Pushing both to 50% roughly quadruples the divisor in the warp length formula, since you're dividing by 0.5 twice, which substantially inflates the total warp yarn required — a sanity check worth running before committing to unusually shrinkage-prone fibers.