Yarns weights and sizes

Hi I live in England and we have a different code! for yarns weights and sizes I'm fine with needles but what tarns are comparable with say Double knit and 3ply. I am looking at some projects in Oneskein by Leigh Radford and #1 and #4 mean nothing to me can you help

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Here are the numbered yarn standards from the Craft Yarn Council's website: http://craftyarncouncil.com/weight.html And here is an information page on how the British "ply" system of yarn weights might compare: http://www.yarnfwd.com/main/tension.html

A good way to compare yarns is to look them up on the web and check the gauge information. This can help you determine if another yarn can be substituted.

3 ply yarn is (sport )weight yarn. good for lightweight accessories or home decor.. the downside of this type of yarn doesnt give you enough for medium to large projects.. keep that in mind,,
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its almost like medium four yarn except not as thick..

this link below should be helpful

http://en.wikipedia.org/wiki/Yarn_weight