Engineering review required: the supplied operation catalogue supports the length calculation and fractional ball equivalent, but has no ceiling operation for automatically calculating whole balls to buy. Register and validate a dimensionless round-up operation before production activation. Decimal display precision is not a substitute for rounding upward. The calculator below implements only the supported arithmetic; the whole-ball formula and examples describe the intended completed behavior.
Artwork creation required: no registered thumbnail asset was supplied. Create and register a 400 × 400 WebP thumbnail, then insert it as the first image block. Match neighboring thumbnails: a cheerful yellow five-point star mascot with hands, no separate legs or feet, a white background, and navy, blue and teal yarn-and-measuring graphics. Renderer integration and functional QA are required before activation.
Enter the original number of balls, the original length per ball, the replacement length per ball and your chosen extra allowance. Use metres for both length inputs; do not mix metres and yards or enter ball weights in grams. This version uses metres because yards are not a registered calculator unit.
The original ball count accepts 0–1,000 in whole-ball steps. Each length accepts 0.1–10,000 metres in 0.1-metre steps. The allowance accepts 0–100% in 0.1-percentage-point steps. These are calculator input limits, not yarn recommendations. The default 10% allowance is illustrative; choose an allowance appropriate to your project and any extra yarn already included in the pattern.
The ball-equivalent result may be fractional. A purchase quantity must be rounded upward to whole balls, with an exact integer left unchanged. Automatic upward rounding is pending engineering implementation.
The Knitting Guild Association’s yarn substitution handout describes multiplying original balls by length per ball, then dividing by replacement length per ball. This calculator extends that length ratio with a user-selected percentage allowance. The allowance is a planning input, not a percentage prescribed by that source. Whole-ball purchasing requires the smallest integer that covers the calculated length.
| Original yarn | Replacement length per ball | Allowance | Required length | Ball equivalent | Whole balls to buy | Purchased length |
|---|---|---|---|---|---|---|
| 8 balls × 125 m = 1,000 m | 150 m | 10% = 100 m | 1,100 m | 7.333333… | 8 | 1,200 m |
| 6 balls × 120 m = 720 m | 180 m | 0% = 0 m | 720 m | 4 exactly | 4 | 720 m |
| 5 balls × 100 m = 500 m | 200 m | 5% = 25 m | 525 m | 2.625 | 3 | 600 m |
| 0 balls × 125 m = 0 m | 150 m | 10% = 0 m | 0 m | 0 | 0 | 0 m |
Matching total length alone does not establish that a substitute will produce the intended fabric. Lion Brand’s substitution guidance recommends making a swatch, checking gauge and assessing the resulting fabric. Use the Knitting and Crochet Gauge Calculator to help compare measurements.
This calculation assumes the original ball count is the amount you want to replace and that the replacement uses the same total length before your allowance. Calculate each colour separately. It does not model changes in gauge, stitch pattern, garment size or multiple strands held together.
Positive replacement length is required for division. If invalid values bypass input bounds, an unavailable result must not be treated as zero. Displayed decimals are rounded for presentation and must not be used to implement the missing ceiling operation.