Aran yarn is considered a category 4, which is a medium worsted weight; the knit gauge, also known as the number of stitches per inch, is 16 to 20 stitches and the crotchet gauge range is 11 to 14 stitches. The gauge or number of stitches per inch in knitting and crocheting largely depends upon the stitching pattern, the needle size, the type of yarn and the stitching tension.
The Craft Yarn Council determines guidelines for yarn categories utilizing the standard yarn weight system. A 4 to 4.5 mm knitting needle or a 5.5 to 6.5 mm needle with crochet is recommended for a category 4 medium weight aran yarn. The larger the needle used, the smaller the gauge or fewer stitches per inch. Most yarn's weight is stated on their ball band. The term Aran is synonymous with Worsted, Afghan or Fisherman.