Wraps per inch is a metric used by spinners and knitters to determine yarn weight. It is measured by wrapping the yarn around a ruler or a specialized tool so the strands lie side-by-side without overlapping or stretching. Counting how many wraps fit into one inch provides a standardized gauge to substitute yarns in a pattern.
I spun this merino to 14 WPI, so it should work perfectly as a DK weight for that sweater.
Related terms
Weight
To add heavy materials to a hem or fabric to improve its drape and prevent it from blowing open.
DK
An abbreviation for double knitting, a medium yarn weight widely used for garments.
Gauge
The number of stitches and rows that fit into a standard measurement of knitted or crocheted fabric.
PPI
An abbreviation for picks per inch, measuring the density of weft threads in a woven fabric.