So I crocheted a swatch. I thought you might be interested in swatching, so I'm going to share what I know. As a bonus, you'll be privy to the awesomeness that is the 'correct' gauge for the London Crochet Bag! Ahahaha!
**If (on another pattern) you see that the gauge is telling you the number of stitches that you should have over a certain number of inches - like 8 stitches = 3 inches - start with more than 8 stitches. I multiply the stitch number by 1.5 (which in my example would give us 12 stitches) to use for a sample swatch. Those side stitches are not an accurate representation of your stitch tension.**
So for those of you who are making a London Crochet Bag, and want to do it 'right', your correct gauge is:
13 stitches = 4 inches
10 rows = 4 inches