1. Use a consistent tool: Wrap your yarn around a ruler, pencil, or a designated WPI tool.
2. Don't stretch: Lay the yarn gently against the tool. Stretching the yarn will give you an incorrect, tighter measurement.
3. Snug, not tight: The wraps should sit side-by-side, touching each other, without overlapping or leaving gaps.
4. Count: Count how many strands fit within 1 inch (2.54 cm).
Tip: Take a few samples from different parts of your yarn to get an accurate average.