First define the part of the material to calculate. On a consistent mass basis, record the weight of each yarn actually retained in that scope and the percentage by weight of its constituent fibres. Add the weight of each fibre across the yarns, then divide by the total fibre weight in the selected scope to obtain its theoretical percentage. Knitting two yarns together does not mean two fibres each make up half. Number of strands, yarn count or purchased weight alone cannot substitute for the mass actually retained.
This calculation helps brands and buyers check development sample or bulk material records when yarn weights and composition data are reliable and their mass bases are consistent. The result describes only the selected scope and assumptions; it is not automatically the measured composition of an entire garment, a legal label, certified content or a sourcing claim. Review final claims against the actual product, evidence and requirements applicable in its sales markets.
Define the scope and collect comparable weights
State whether the calculation covers a swatch, the garment body, a sample in one size or specific parts of an agreed batch. List which yarns, ribbing, sewing threads and other components are included or excluded. If different parts use different yarns, record them separately; do not present the body result as the entire sweater's result. For each yarn group record article number, lot, fibre composition and percentages, weight retained in the scope, basis of mass and date.
Weights must use the same units and comparable conditions, compatible with the mass basis of each yarn's composition percentages. Yarns may contain different moisture or finishing substances. Purchased weight, damp sample weight and fibre mass adjusted by a particular method cannot be mixed directly without verification. Ask the supplier or laboratory which weighing, conditioning or correction method was used and retain records. If bases differ or cannot be confirmed, align the method before calculating; do not pass off an assumed correction factor as a test result.
Yarn count, strand count and consumed weight differ
Yarn count describes information related to yarn fineness, while the number of strands says how many yarns are used together. Neither is the percentage by mass of fibres in the garment. Even when two yarns are knitted together, linear density, length used, construction, garment sections and process losses may differ. An equal number of strands does not itself prove equal weight. First establish the mass of each yarn group that actually enters and remains in the selected scope, then split it according to that yarn's own composition.
Do not use the purchased weight of whole cones directly as a sample or garment's yarn weight. Remaining yarn, knitting waste, trimming and rework can change the relationship between input and retained quantity. If estimating by subtracting them from input, ensure they apply to the same scope and are not deducted twice. Do not enter unconfirmed losses as zero or treat a general loss rate as actual WTBF or style data.
Hypothetical example: a defined scope using two yarn groups
This is a mathematical example, not a WTBF product, actual yarn test or garment label. Assume a specified swatch ultimately retains 100 grams of yarn, excluding components outside that scope. All weights and composition percentages use the same comparable mass basis; assume the stated weights are net fibre mass, without moisture or other non-fibre substances. The first group is 70 grams of pure cotton yarn. The second is 30 grams of blended yarn, assumed by weight to be 50% cotton and 50% viscose fibre. The 70 grams and 30 grams are quantities ultimately retained, not quantities purchased; no additional loss is deducted.
| Yarn group | Weight retained in this scope | Assumed yarn composition | Cotton fibre weight | Viscose fibre weight |
|---|---|---|---|---|
| First group | 70 grams | 100% cotton | 70 grams | 0 grams |
| Second group | 30 grams | 50% cotton, 50% viscose | 30 × 50% = 15 grams | 30 × 50% = 15 grams |
| Total | 100 grams | Both yarn groups combined | 85 grams | 15 grams |
Cotton is 70 + 15 = 85 grams and viscose is 15 grams. With 100 grams of fibre mass in the selected scope as the denominator, the theoretical result is 85% cotton and 15% viscose. If yarn composition or actual retained weights change, recalculate rather than continuing to use this example. With more than two yarn groups, still split each group by its weight and composition, combine like fibres and divide by total fibre weight in the same scope.
Use records to distinguish plans, actual quantities and tests
Planned usage may come from sample or process information but should be marked as an estimate. During production, record actual yarn issued, recovered leftover yarn and identifiable waste for the agreed scope, checking lots and units. These records can help estimate retained weight, but input minus leftovers and waste is meaningful only when records are sufficiently complete and the deductions cover the same scope. If issue records cover multiple garments or sizes, reliable allocation evidence is also needed; do not present a batch average as a measured value for each garment.
Record whether fibre composition in the yarn source documents is expressed by weight, and note the version and applicable lot. Recheck if supplier, lot, composition or knitting method changes. Necklines, cuffs, panels, linings, trims or other materials can have different compositions and may require separate treatment under applicable rules. List their relationship to the calculation scope first, then have the responsible person decide which further data or tests are needed. Do not assume they are all included or all excluded.
| Record field | Question to check |
|---|---|
| Object and version | Which swatch, section, size or batch is covered, and which specification version applies? |
| Each yarn group | What are its article number, lot, fibre percentages by weight and supporting documents? |
| Mass and condition | Is this purchased, input or retained weight? Are units and weighing, conditioning or correction bases consistent? |
| Differences and allocation | How are leftovers, waste, rework and other uses recorded, and are deductions duplicated for the same scope? |
| Conclusion and next steps | Where does the result apply, which components, evidence or tests remain unconfirmed, and who approves the next step? |
If the source records cannot support an estimate of yarn mass within that scope, obtain verifiable data or mark the result pending. Buyer, supplier and selected laboratory should agree the test requirements, sampling, applicable method, fees and use of results for the project. This guide does not claim WTBF has tested any product.
Labels and sourcing claims require separate review
The US Federal Trade Commission's textile labelling guidance explains that covered products must disclose fibre names and percentages by weight; distinct sections of different composition may need separate disclosure where applicable, and some components may have exceptions. The scope depends on the product and applicable rules. Do not automatically print the swatch calculation above as an entire garment's label. This US guidance is not a universal labelling rule for all markets.
The EU textile label guidance describes fibre-composition marking for products placed on the EU market. Have the person responsible for each target market check applicable fibre names, sections, languages, test basis and label versions; confirm other markets separately. A content percentage is also different from geographic fibre origin or a certification claim. Calculating a percentage does not prove a particular origin or certification attribute. For evidence chains see the fibre sourcing claim guide; for multi-market artwork and review see the composition and care label guide.
What to include in an inquiry
Use the WTBF inquiry page to provide the style reference, yarn article numbers and proposed compositions, expected usage and mass basis for each yarn group, sections and sizes covered by the calculation, quantities per style, colour and size, intended sales markets, proposed claims and any testing requirements. Browse knit pullovers for style references. Ask the supplier what material records, samples and usage evidence can be supplied and which testing, quotation and scheduling items require separate confirmation. Final garment composition and claims need review against actual evidence.