I purchased the pattern #73 women's top down short sleeved cardigan from you and was hoping to be able to use yarn I have the my gauge is 10 stitches to 3 inches. I was thinking of making the smaller size and using this yarn. It is a softee chunky yarn with a gauge on the label of 15s and 20r for 4x4. Any advice??
Yarn substitution can be tricky if you really want to use a yarn from your stash.
The most important thing is to match the pattern's gauge; however, it's also important to consider and try to closely match the weight and nature of the yarn.
-- substituting a medium weight yarn for a bulky weight yarn will cause the stitches to look looser, which may be fine if the new yarn has some mohair or other fluffy fiber in it that will fill in the space;
-- substituting a boucle yarn for a basic, plied yarn will change the look of the finished project (like obscuring any fancy stitch textures or lace patterning) and may give you an inconsistent gauge;
-- substituting a heavier cotton yarn for a lighter weight synthetic blend will affect the drape and overall weight of a project;
-- substituting a marled or ombre colored yarn for a solid color yarn will make it harder to see delicate stitchwork;
Things like this should be taken into consideration when choosing a yarn substitution. However, the best test will be to knit a swatch (which you have to do to see if you can match the pattern gauge) and see if you like the effect of the yarn substitution.
In your specific example, the pattern is calling for a bulky weight yarn, which is defined (by www.yarnstandards.com, a commonly used standard) as a yarn which knits to a gauge of 3 to 3.75 sts per inch on size 9 to 11 needles.
You yarn seems like a bulky yarn at 15 sts = 4" or 3.75 sts = 1", so that's a good start.
Next step is to see if you can match the gauge called for in the pattern exactly, then you can most likely get good results with your substitution.
The gauge for pattern #73 is 8 stitches = 3” [7.5cm] and approx. 17 rows = 4” [10 cm] on size 11 needles.
Knit a swatch on size 11 needles and see if you meet the gauge. Be sure to measure it flat and not while the stitches are still on your needle. If you are a little off, you may be able to change to a needle size bigger or smaller and knit a new swatch. It's not important what needle size you need, as long as you can achieve the desired gauge.
Once you do match the gauge, you can pretty safely go ahead and feel confident in your substitution.
NOW, if the gauge is a little off, and you still want to use the yarn... you may be able to just knit a smaller or larger size to "make up" for the gauge being off. This approach can work, but I don't generally recommend it for any projects where the shaping is precise.
Pattern #73 is a top-down pattern which has very specific rows required to complete the raglan shaping from the neck down to the underarms. If by substituting a yarn that gives a different gauge and knitting different size to compensate, you end up with too few or too many rows once you've completed the shaping the the underarms, you would then need some pattern expertise to know how to continue and make the pattern work from there. I think most beginners would not want this challenge.
For more on measuring and matching gauge... you can see this previous post on this same topic at: http://sweaterbabe.com/WordPressBlog/knitting-questions-and-how-to/yarn-substitution-and-measuring-gauge-part-i/.