The above are popular yarns – other yarns may well produce different values, especially if they aren’t 100% wool: for example, 900yds of Malabrigo Chunky (bulkyweight, 100% wool) is 900g, and 900yds of Knit Picks Billow (bulky weight, 100% cotton) weighs 750g.
If you have a ballband for this yarn, you can calculate the weight of 900yds by:
If you want to use cotton, you should look for mercerised cotton. This has been treated to produce a non-fuzzing, slightly shiny appearance which is perfect for lace.
You might also look at blends with linen, hemp, nettle, or silk. There are also some remarkable yarns around which are cotton-like, but are made from bamboo, milk protein, crab shells … the world’s your oyster (and there’s also pearl yarn!).
Do not disdain wool: there are many wools around that are soft to the skin, and have wonderful stitch definition which is perfect for crochet. Specific breeds that are good are Blue-Faced Leicester and Falkland – I can particularly recommend Eden Cottage’s BFL Bowland and Debbie Bliss Falkland Aran – I designed this in Falkland Aran:
Incidentally, Ravelry is a great resource for learning about yarns. You can select to look at different weights, fibres, blends, sources, etc., and even look at projects worked in any yarn that interests you. Another great website is Yarnsub – especially if the price-tags on some yarns scare you! It’s still in its early stages, but still good. It was designed to help substitute yarns recommended in patterns if they were discontinued, hard to find, allergenic, or just to darn expensive!
In addition to Yarnsub, you can look up the pattern on Ravelry. Click on ‘yarn ideas’ or ‘projects’ to see what other people have used to make this pattern.
This has the advantage that you can see what the pattern looks like made up in the different yarns, and read the crafters’ notes – some of which can be extremely helpful in making your choice.
Ultimately, the yarn you use will have an impact on the finished product. Cotton will make a heavy blanket, and may ‘grow’ when it’s washed. Acrylic can be soft and easy-care, but can look threadbare and thin after a few washes. Non-superwash wools can felt! You’ll need to swatch and launder to ensure you get the same gauge as the pattern and the feel you want – sometimes more than once.