Jacinda, I'm afraid we're not going to be much help.

Ply refers to how many strands of yarn are twisted together to make a yarn, but there is no standard as to how thick each ply is. When I was a teenager and someone referred to 4 ply, you could be reasonably sure that meant worsted weight, but not anymore. We generally assumed that 2 ply was baby yarn, but that is not always the case either. Some bulky yarns are just 2 ply.

Possibly you could check Yarndex out and compare the yarn asked for in the pattern and see what the gauge for that yarn is. I think that will probably be the most help I can give you.

Here is a link that might be useful: Yarndex

Thanks donna but that was no help, the brands I use aren't on there! Could you then maybe give me a rough estimete eg the thinnest to thickest i.e is fingering weight thinner than DK? Is worsted a bulky wool and thicker than DK? Could I assume that a fingering weight would refer to a 3,4 or 5 ply, a DK to 8 ply and worsted to a 10 or 12 ply? (Roughly...?) Your help would be much appreciated!

Jacinda, I found this information online:

Laceweight, or 2-ply/3-ply: Although some sources say differently, generally speaking, 2-ply/3-ply yarns are very fine, almost threadlike yarn that are used for lacy garments such as shawls and scarves, and baby clothes.

Fingering Yarn, or 4-ply: Also called "5-ply" in Australia and New Zealand, this yarn is also used for baby clothes and lacy garments, but is also used for Fair Isles and adult garments. (Granted, adult garments will take a long time to complete with such a fine yarn!) Since this yarn is fine, greater detail can be achieved when knitting a picture or motif into the garment. (In a different resource book, fingering weight yarn was considered the same as 2-ply and 3-ply yarn.)

Sportweight, or DK (Double Knitting):This yarn is also "8-ply" in Australia and New Zealand. This versatile yarn is used for all types of garments worn from infancy through adulthood. It can be knitted up into lacy garments as well as garments with lots of texture and cables, and everything in between. There are many patterns available for this weight of yarn and it is very popular. It comes in many colors, and is also available with different effects, i.e. tweed (different flecks of color), heather (colors that are finely blended with paler shades for a gently speckled effect), brushed (fuzzy effect), and others.

Aran, Worsted, or Triple: Also referred to as "knitting worsted" or 12-ply in Australia and New Zealand, this yarn is generally used for heavily textured garments involving cables and other such texture techniques. It used to only be available in natural unbleached shades of creamy white and ivory, but it is now available in many colors although the white is the traditional choice for the knitting of an Aran sweater.

Chunky, or Bulky: 14 ply in Australia or New Zealand, this is heavy yarn that knits up quickly on large needles, and is often the choice of beginners since it is easy to handle and fast work. It comes in a wide range of colors, and is popular for oversized sweaters, jackets, and children's wear.

Donna- Thank you thank you thank you!Makes a lot of sense!

We also consider fingering weight to be sock weight.