Yarn Weight Conversion Calculator
Identify a yarn's weight class from wraps per inch.
Identify a yarn's weight class from wraps per inch, with the gauge range and needle size each class implies.
Wind the yarn round a ruler, strands touching but not squashed, and count how many fill one inch.
Yarn weight
Light / DK
Craft Yarn Council 3
Wraps per inch is the best method without a ball band but it is not exact: a loosely spun woolen yarn and a tightly spun worsted-spun one can wrap the same and knit quite differently. Confirm with a gauge swatch before starting a garment.
How the Yarn Weight Conversion Calculator works
Yarn without a ball band is a common problem — a destashed cone, an inherited bag, a partial ball with the label long gone. Wraps per inch answers it: wind the yarn round a ruler without stretching or overlapping, count the wraps in an inch, and the number places it in a weight class more reliably than eyeballing the thickness.
Also known as: wraps per inch calculator · WPI calculator · yarn weight chart
How wraps per inch works
Wrapping yarn round a ruler with the strands touching but not compressed gives a direct measure of its diameter: if twelve wraps fill an inch, each strand is a twelfth of an inch thick. That maps onto the standard weight classes, which are defined by thickness.
The Craft Yarn Council numbers the classes 0 to 7 — lace, super fine, fine, light, medium, bulky, super bulky, jumbo — and the ones most patterns use are 1 through 4: fingering, sport, DK and worsted.
The classes overlap at their boundaries by design, because yarn thickness is continuous and the categories are not. A heavy DK and a light worsted genuinely are interchangeable for many purposes.
A worked example
An unlabelled cone wraps twelve times per inch. That places it in the light/DK class, which suggests 21 to 24 stitches over four inches on a 3.75 to 4.5 mm needle.
Those are starting points, not answers. Swatching at 4 mm and finding 22 stitches over four inches confirms it; finding 26 says the yarn is finer than the wrap count suggested, which happens with tightly spun yarns.
Where the answer misleads
Wrapping tension is the main source of error, and it is entirely in your hands. Wrapping tightly compresses a soft yarn and inflates the count; wrapping loosely leaves gaps and deflates it. Wrapping three times along the yarn and averaging helps, because yarn is not uniform.
Spin matters as much as diameter. A loosely spun woolen yarn and a tightly spun worsted-spun yarn can wrap identically and knit to quite different gauges, because the woolen yarn compresses under the needle and the worsted-spun does not.
The class is a shopping aid, not a specification. What decides whether a yarn works for a pattern is a blocked swatch at the pattern's gauge, and nothing about wraps per inch substitutes for that.
Frequently asked questions
How do I measure wraps per inch?
Wrap the yarn round a ruler or a WPI gauge so the strands sit side by side, touching but not squashed, and count how many fill one inch. Do it three times along the yarn and average, since yarn is not perfectly consistent.
What are the yarn weight classes?
The Craft Yarn Council numbers them 0 to 7: lace, super fine, fine, light, medium, bulky, super bulky and jumbo. Fingering is 1, sport is 2, DK is 3 and worsted is 4 — the four most commonly used.
Is wraps per inch reliable?
It is the best method without a label, but it is not exact. A loosely spun woolen yarn and a tightly spun worsted-spun one can wrap the same and knit quite differently, so confirm with a gauge swatch before starting a garment.
Can I substitute across weight classes?
Sometimes, since the classes overlap at their boundaries — a heavy DK and a light worsted are often interchangeable. What matters is meeting the pattern's gauge with a fabric you like, not the number on the band.