WPI to Yarn Weight

How to use

1. Wrap your yarn around a ruler or a pencil, laying each wrap snugly next to the last without squashing them together or leaving gaps.
2. Count how many wraps fit into one inch, then unwind and enter that number.
3. Read the result — the yarn weight category, plus the gauge you can expect from it.
4. If your count sits right on the boundary between two categories, treat the yarn as somewhere between the two and let a swatch decide.

Good to know

• Wrap snugly but do not stretch or compress the yarn. Pulling it tight squashes the plies and reads thinner than the yarn really is, which is the most common source of a wrong answer.
• Wrap over at least two inches and divide, rather than counting a single inch. A longer run averages out the unevenness in the yarn and in your wrapping.
• The boundaries between categories are not universal — different sources place them a wrap or two apart, and this chart picks one common set. A value near a boundary is genuinely ambiguous, not a precise answer.
• WPI describes thickness, not fibre or construction. A fuzzy mohair and a smooth mercerised cotton can wrap identically and still behave completely differently in a fabric, so treat this as a starting point and swatch.

FAQ

What does WPI mean?

Wraps per inch — how many strands of the yarn lie side by side in one inch when wrapped around a ruler. Thinner yarn fits more wraps into the inch, so a high number means a fine yarn and a low number a thick one.

How do I measure wraps per inch properly?

Wrap the yarn around a ruler so each wrap just touches its neighbour — snug, not stretched, and not squashed. Count over two inches and halve the number for a more reliable reading than a single inch gives.

My count falls between two weights. Which one is it?

Genuinely between the two. The chart boundaries vary by source, so a borderline value is not a precise answer — knit a swatch and compare the gauge against both categories to decide.

Can I use WPI instead of knitting a gauge swatch?

No. WPI tells you roughly how thick the yarn is, which is enough to pick a starting needle size and to work out what a pattern expects. Gauge is about the fabric you actually make, and only a swatch shows that.

Does WPI work for handspun yarn?

Yes, and it is one of the main reasons the technique exists — handspun has no ball band. Bear in mind handspun is often less even than mill yarn, so wrap over a longer run and expect a rougher estimate.