Free tool · no sign-up · works offline once loaded

WPI calculator: find yarn weight from wraps per inch

Identify a mystery yarn from its wraps per inch, and convert yarn weight names between US, UK, Australian ply and the Craft Yarn Council 0–7 numbers.

Wraps counted

Over a length of

Unit

Wrap more than an inch and count it all: 22 wraps over 2 inches is more accurate than 11 over 1. Keep the wraps touching but not squashed.

Yarn weight conversion chart

No.	US / CYC	UK	Australia / NZ	WPI	Knit gauge per 4 in	Needles

Categories, gauges and needle ranges follow the Craft Yarn Council’s Standard Yarn Weight System. WPI ranges are commonly used guides and overlap at the edges.

How to measure wraps per inch

You need a ruler and the yarn. Some people use a WPI tool, a small notched card or wooden gauge, but a pencil works just as well: wrap the yarn round it, then lay a ruler along it and count the strands in one inch.

Wrap with the same light tension you knit with. Pulling hard makes the yarn thinner and adds wraps; leaving gaps removes them. Measure in two or three places and use the average.

One yarn, many names

Yarn weight names differ by country. The Craft Yarn Council numbers its categories 0 to 7, the UK uses names such as 4 ply, DK and aran, and Australia and New Zealand count plies, where 8 ply means DK rather than eight strands. The chart above lines them up.

Once you know the weight, pick a starting needle or hook in the needle size converter or hook size converter, and estimate how much you need with the yarn yardage calculator.

How to use it

Wrap the yarn around a ruler or a pencil, laying each wrap snugly beside the last without overlapping or stretching it.
Wrap at least one inch (or a few centimetres) and count the wraps.
Enter the number of wraps and the length they cover.
Read the yarn weight, its UK and Australian names, and the needle and hook sizes to start with. Confirm with a swatch.

Questions

What does WPI mean in knitting?

WPI stands for wraps per inch: how many times a strand of yarn fits side by side across one inch. Thinner yarn gives more wraps. It is a quick way to estimate the weight of yarn that has lost its label.

How many wraps per inch is worsted yarn?

Worsted and aran (medium, 4) yarn usually gives 9 to 12 wraps per inch. DK (light, 3) gives about 12 to 15, and bulky (5) about 6 to 9.

What is DK yarn in US terms?

UK DK (double knitting) matches the Craft Yarn Council’s Light (3) category, also called light worsted in the US and 8 ply in Australia and New Zealand.

Is aran the same as worsted?

Both are in the Medium (4) category, but aran is slightly thicker. Worsted sits between UK DK and aran, so swatch when you swap one for the other.

Why do my WPI and my swatch disagree?

Wraps per inch only measures thickness. Fluffy, brushed or loosely plied yarn compresses when wrapped, and dense yarn does not, so two yarns with the same WPI can knit to different gauges. Always trust the swatch.