Work back from your finished measurement to the pre-wash (as-knit) length your knitter should target, apply a shrinkage percentage to find the after-wash size, or read the real shrinkage from a washed swatch. The arithmetic is exact — but the shrinkage rate is an assumption until you confirm it on a real sampling wash, so treat the output as a planning figure and lock it at sampling.
⚠️ Indicative — confirm on a real sampling wash. The formulas here are exact, but the shrinkage percentage you enter is your own figure: actual shrinkage changes with fibre, gauge, knit structure, wash temperature and drying. Knits also relax mostly on the first wash. Measure a washed swatch of your own fabric and lock the number at sampling before you spec bulk.
Pre-wash length, finished size and shrinkage % are three views of the same equation. Fix any two and the tool solves the third — so it works whether you're planning, checking or measuring.
Most knitted fabric loses length — and sometimes width — on its first wash. To hit spec, the as-knit piece has to be made slightly larger than the finished measurement, and that gap is exactly the allowance this tool sizes.
The arithmetic has no error margin. The shrinkage % you feed it does — it's an assumption until you confirm it on a real sampling wash of your yarn and wash cycle.
Shrinkage is roughly proportional, so once you know the %, run each key dimension — body length, sleeve, chest — through the pre-wash mode to build a clean, washable graded spec.
No black box — here is the exact math the tool runs, with shrinkage s written as a percentage:
pre-wash = finished ÷ (1 − s/100) finished = pre-wash × (1 − s/100) shrinkage % = (before − after) ÷ before × 100 Worked example: a 60 cm finished body length at 5% shrinkage needs 60 ÷ 0.95 = 63.2 cm knitted before washing. That 3.2 cm is the allowance your knitter adds so it relaxes back to 60 cm.
A planning guide to what moves the number — none of these is a guaranteed figure, so always test:
| Factor | What it does to shrinkage |
|---|---|
| Fibre | Natural fibres like cotton and wool generally relax and shrink more than synthetics such as acrylic or polyester; wool can also felt if agitated or washed warm. |
| Knit structure | Looser, chunkier and heavily textured knits tend to relax more than tight, fine-gauge fabric. |
| Wash & dry | Hot water and tumble drying pull far more shrinkage than a cool, flat-dry cycle — and the first wash usually moves the most. |
| Mill finishing | Steaming, pressing and relaxing at the mill remove much of the potential shrinkage before the garment ever ships. |
Costing the program too? Pair this with the knitwear cost calculator and translate your yarn spec with the yarn count converter, then split each colourway across sizes using the size run calculator. New to sourcing? See our knitwear manufacturer overview.
Wash a knitted swatch or sample, measure a dimension before and after, and divide the difference by the before-wash figure: shrinkage % = (before − after) ÷ before × 100. Do this on the exact yarn and wash cycle you plan to use in production, because shrinkage varies by fibre, gauge and laundering. Then work backwards to the pre-wash length your knitter should target so the washed garment lands on your finished spec.
Divide the finished measurement by one minus the shrinkage written as a decimal: pre-wash = finished ÷ (1 − shrinkage%/100). For a 60 cm finished body length at 5% shrinkage, that is 60 ÷ 0.95 = 63.2 cm as-knit. Knitting straight to the finished number is the classic error — the garment then comes up short after its first wash.
It depends entirely on the yarn, knit structure and how the piece is washed, so there is no single figure — natural fibres like cotton and wool usually move more than acrylic, and hot water or tumble drying pulls far more shrinkage than a cool, flat-dry cycle. Most of the movement also happens on the first wash. Treat any published range as indicative only and confirm the real number on a sampling wash of your own fabric before you commit a spec.
List the finished (after-wash) measurements as your spec — that is what the customer receives — but also give your maker the pre-wash, as-knit target and the shrinkage you allowed for, so knitting and washing can be set to hit it. At Kiwi Giyim we confirm shrinkage on your approved sampling before bulk, and our MOQ is 250 pieces per colour, per size, so it pays to lock the numbers at the sampling stage.
Send your tech pack (or use our free template) and we'll confirm shrinkage on your approved sampling, reply within one business day with real pricing, and set the as-knit targets so bulk lands on spec after washing.