# Yarn Weight Converter

> Yarn weight converter: US names to wraps per inch and needle size. Free yarn weight converter with the formula shown - runs entirely in your browser, no signup.

- **Canonical URL:** https://boringtoolskit.com/yarn-weight-converter/
- **Category:** Converters
- **Evidence level:** authored-methodology
- **Reviewed:** July 26, 2026
- **Last verified:** 2026-10-12
- **Privacy:** Inputs and results stay in this browser unless the page clearly labels an external request.

## How it works

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

- 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.

## Common 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.

## Related tools

- /mm-to-inches/
- /yards-to-meters/
- /grams-to-ounces/

## Sources

- [Standard Yarn Weight System](https://www.craftyarncouncil.com/standards/yarn-weight-system)

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