Throughout the steps below Julie uses the example of an Emma Version A that her daughter knit with a finer weight yarn.
Please note that this technique may not work with other knit designer's patterns, this trick specifically works with ours because of the way our patterns are sized.
Julie's daughter knit a swatch with the yarn she wanted to use for the Emma Version A and got a gauge of 4 sts per inch. In the book it recommends 3 sts per inch.
When you determine you have a different gauge, simply go to the schematic section of the pattern and find the bust circumference of the size that you would like. In this example, she wanted to knit a medium which has a bust circumference of 37.5"
Simply multiply your gauge to the desired circumference. In our example, because her gauge was 4sts per inch and she wanted 37.5" bust circumference we learned she needed 150 sts at the bust with the following equation. 4 (sts per inch) x 37.5 (desired bust circumference) = 150 sts
Now simply find the size that has the proper stitch count for your bust. For the Emma pattern this count will be after you've finished your seamless yoke, placed the sleeve stitches on hold, and cast on stitches for the underarm. We can find this count on page 64 of the Cocoknits Sweater Workshop, in the second paragraph down. In this section it is only describing the back stitch count, so it is half of our total sts needed. 150 / 2 = 75. "Next round knit 50 (56, 62, 68, 74)." The 2x is the closest at 74 sts, so in order to knit the sweater in our new gauge we simply knit the size 2x rather than the medium. It's that easy!
Please note: this won't work with everyone's gauge if it's significantly different than the pattern. For example, if you want to knit the Emma in a lightweight yarn with a tight gauge it may be better to simply work from the Molly pattern which was designed for lighter weight yarn. But if you're just a little off with gauge, this is a very simple fix!