Calculator
Yarn Held Together Calculator
Pick the yarn weight of each strand you're holding together and we'll tell you the effective weight of the resulting yarn — so you can match it to your pattern.
Calculator
How this works
Yarn weight categories (lace, fingering, sport, DK, worsted, bulky, super bulky, jumbo) are loosely defined by stitches per inch — but the underlying physical property is yarn diameter, and an easier proxy for diameter is wraps per inch (WPI). The thinner the yarn, the more wraps fit in 1 inch of ruler.
When you hold two or more strands together, the strands lie side by side and the bundle's diameter is roughly the sum of the individual diameters. So the combined WPI is:
combined WPI = 1 / (1/WPI₁ + 1/WPI₂ + ... + 1/WPI_n)
It's the same shape as the formula for resistors in parallel — the reciprocal of the sum
of reciprocals. For two equal strands it simplifies to WPI / 2, which
matches the knitter rule-of-thumb "two strands held together is about one weight
category heavier" but with the math behind it.
Why this matters
Patterns specify a yarn weight because it determines the gauge, drape, and fabric feel. If you want to substitute by holding two thinner yarns together — to use stash yarn, to mix colors, or because you can't find the called-for weight — you need to know whether the combination actually matches. This calculator gives you a quick sanity check before you commit to a project.
A note on accuracy
WPI category boundaries are pragmatic, not strict — real yarns span boundaries based on tension, twist, and ply. The calculator gives you the closest category, but treat boundary results as approximate. Always knit or crochet a small swatch before committing to a project. If your combined WPI lands on a boundary, the gauge converter can help you adjust the pattern numbers if your swatch comes out slightly off.
Tips
- To measure WPI, wrap your yarn around a ruler (or a pencil with a known diameter) without overlap or stretching, then count wraps per inch.
- Two strands of the same weight usually moves you one category heavier (two fingering ≈ sport-to-DK; two DK ≈ bulky).
- Three or more strands can match a much thicker target — three fingerings ≈ worsted-DK territory.
- Mixing weights (e.g., fingering + worsted) gives something in between but closer to the thinner strand — the bulky one dominates the bundle diameter.