Calculated in your browser; your inputs are not sent to us. Privacy
Results update when you run the tool.
This tool processes the selected input in your browser. Review the output before relying on it; format and file behavior can vary by browser and source data.
Your inputs and results stay in this browser. This page may send privacy-bounded aggregate interaction events described in Privacy; it does not send your entered values or result contents.
Use this result
Share the current inputs or ask ChatGPT to explain the calculation in context.
More options
What does this converter do?
US weight 4 converts to Worsted weight yarn, which calls for 4.5 to 5.5 mm needles. Start with 5 mm, knit a swatch, and change needle size until your stitches per 10 cm match the pattern, because two yarns with the same weight 4 label can still knit up differently.
How the US yarn weight scale works
The Craft Yarn Council standard sorts yarn into eight numbered categories, from 0 (Lace) up to 7 (Jumbo). Each number describes strand thickness, and each category carries a suggested needle range in millimeters. The converter reads your number and returns the category name plus that range: 0 Lace and 1 Fingering at 2.25 to 3.25 mm, 2 Sport at 3.25 to 3.75 mm, 3 DK at 3.75 to 4.5 mm, 4 Worsted at 4.5 to 5.5 mm, 5 Bulky at 5.5 to 8 mm, 6 Super bulky at 8 to 12.75 mm, and 7 Jumbo at 12.75 mm and up.
Regional names for the same thickness vary widely. A yarn sold as 8-ply in Australia or double knitting in the United Kingdom usually lands at US weight 3, and chunky yarns abroad often match US weights 5 or 6. Converting a label to the US category and its needle range gives you one common language for patterns, substitutions, and shopping.
Why a gauge swatch beats the label
The needle ranges in the converter are starting points, not guarantees. Two yarns can both carry a weight 4 label and still differ in ply, twist, and fiber, which changes how many stitches you get per 10 cm. Patterns state a target gauge, such as 18 stitches and 24 rows over 10 cm, and hitting that number matters more than the category printed on the ball band.
Knit a small swatch in the stitch pattern your project uses, wash and block it the way you plan to treat the finished piece, then count stitches over 10 cm. If you get more stitches than the pattern calls for, move to a larger needle; if you get fewer, go smaller. A short swatch protects hours of work, so treat the converter result as the first needle you try rather than the last one you need.
How this calculator works
Formula
Enter a US yarn weight number from 0 to 7 and the converter looks up the matching Craft Yarn Council category name and its recommended needle size range in millimeters. Weight 0 (Lace) pairs with 2.25 to 3.25 mm needles, weight 4 (Worsted) with 4.5 to 5.5 mm, and weight 7 (Jumbo) with 12.75 mm and up. Entries outside 0 to 7 are rejected as invalid.
Worked example
A skein labeled US weight 3 converts to the DK category, so its needle range is 3.75 to 4.5 mm. Start with 4 mm needles, cast on roughly 22 stitches for a 10 cm swatch, and adjust up or down until your stitch count matches the pattern gauge.
Assumptions to verify
- The input is a whole-number US Craft Yarn Council weight from 0 through 7; values below 0 or above 7 are out of range.
- Needle sizes are given in metric millimeters using the standard category pairings, not specific US needle numbers.
- The returned needle range is a starting point only; a gauge swatch on your actual yarn decides the final needle size.
Frequently asked questions
What is US yarn weight 4 in other naming systems?
US weight 4 is Worsted weight, often labeled Aran or 10-ply outside the United States. It calls for 4.5 to 5.5 mm needles and is the most common all-purpose weight for sweaters, blankets, and hats.
Why do weight 0 and weight 1 show the same needle range?
Both Lace and Fingering yarns sit at the thin end of the scale and work on 2.25 to 3.25 mm needles. The difference is strand thickness, so lace weight produces more stitches per 10 cm than fingering on the same needle.
Can I skip the gauge swatch and trust the label?
Labels give a suggested range, but ply, twist, and fiber make two weight 4 yarns behave differently. Use the converter result to pick a first needle, then knit a swatch and match the pattern stitch count before you start the real project.
Cite this tool
BoringToolsKit. “Yarn Weight Converter.” boringtoolskit.com/yarn-weight-converter/. Free to reference in articles, syllabi, and answer posts with a link.
Privacy: Inputs and results stay in this browser. Any future sponsored recommendation or advertisement will be clearly labeled and kept separate from the calculation.