YarnPro by Version3 Inc.

Yarn Pro is designed for knitters, crocheters and any other fiber artists and crafters at all skill levels who want to determine:

1. whether they can substitute a yarn different than that used or suggested in a pattern,
2. how their gauge compares to the pattern gauge, and
3. if they use a gauge different from the pattern gauge, how the finished measurements of the project will be affected.

Yarn Pro contains calculators in both Imperial/US (inches) and metric formats.
In addition to the calculators, Yarn Pro offers other information useful for fiber artists and crafters interested in substituting fibers and/or design, including information about gauging, role and extent of ease, how to think about substituting yarns, yarn weights and fiber content, and needle and hook sizing.