I’ve noticed that lighter weight yarns have a consistent thickness whether working with luxury natural yarns or inexpensive acrylic. But Bulky luxury yarn works up much smaller than Bulky acrylic yarn.
For example, I made Mama Ming with Woolike Chunky. For that project I need to use an I-9/5.5mm hook and about 250g of yarn. But for Tammy Junior I used a G-6/4.25mm hook and she only took about 150g of Malabrigo Mecha. Both yarns are classified as Bulky (5).
Large manufacturers like Lion, Bernat, or Loops & Threads follow the guidelines of the Craft Yarn Council. CYC bases its guidelines on recommended gauge & needle/hook size.
Luxury and small batch manufactures base their yarn weights on the actual width of the yarn, measured by the wraps per inch (wpi) – the actual number of times you can wrap the yarn around a ruler in 1″. It is easier to visualize 6 wpi than 1/6th”.
Using wpi instead of recommended gauge/needle size gives a better idea of the yarn. While the recommended gauge/needle/hook size is similar for both Malabrigo Mecha & Woolike Chunky, the wpi are different: Malabrigo Mecha: 8 wpi & Woolike Chunky: 5-6wpi.
Since 5-6wpi is the wpi of many Super Bulky yarns, I treat Woolike Chunky as a Super Bulky yarn in my patterns.