Some rainy-day thoughts about gauge...
There are some aspects of gauge which never seem to be discussed on KnitU or the KnitList.
Specifically, the fact that the suggested gauge on the yarn's ball band may not be suitable for the project you, the knitter, wish to create on your own.
For example, the gauge suggested on the ball band for most worsted weight yarns generally will produce a fabric that drapes in a manner suitable for a sweater. However, if you are designing your own shawl, you may want a slightly looser gauge. And if you are designing an afghan, you will want a slightly denser fabric. A knitted afghan done at sweater gauge may be a bit too loose and stretchy to be used as a blanket. If you are designing a pair of thick hiking socks using worsted weight yarn, you will want an even denser gauge, or the socks will wear too quickly, and may not be elastic enough to stay up on your leg.
So, the real secret to a good fabric when you are designing your own garment is to swatch, regardless of what the ball band says, changing needle sizes, until you arrive at a fabric that feels appropriate for what you want to do with the yarn. THEN count the number of stitches per inch -- the number of stitches per inch that produced the desired fabric YOU want to work with. And finally, multiply THIS number by the number of inches in width (or circumference) needed for your garment.
The best swatch to give you a sense of what the fabric will be like should be at least 40 stitches wide, and at least 3 or 4 inches long, IN PATTERN. Don't like it? Change needle sizes until it produces the feel and drape you want to achieve for the item you want to make.
This is a very simple concept, yet I see so many knitters disappointed with the item they produced because they swatched until they got the gauge suggested on the ball band, and then designed their garment using THAT gauge, only to end up with a stiff shawl or a droopy afghan.
It's good advice to use the suggested gauge on the ball band only if you are going to make an item the yarn was designed for. If you are going to make anything but socks with sock yarn, swatch until you get the fabric you like, measure ITS gauge, and do your math from there.
This concept seems to be even more lost in crochet. Crochet, by its nature, is thicker and less elastic than knitting because you are actually tying a KNOT with each stitch. Granted, you are making a series of connected knots, but they are knots nonetheless. I often feel the suggested crochet gauge on most yarn ball bands will produce a fabric that is too stiff. Again, change hook sizes until the fabric feels right to YOU. And make a swatch at least 6 or so inches wide, and work for at least 3-4 inches before you consider whether or not you like the resulting fabric. Change hooks sizes if you don't. Anything smaller won't give you a feel for the resulting fabric.
I see a lot of gauge and swatch discussion on the knitting sites on the Internet, but seldom do I see the topic discussed on crochet sites. I have no idea why, but perhaps this explains all the Mile-A-Minute afghans out there that are so thick and inflexible, they could be used for fall mats in karate class.
Many knitters and crocheters seem to view the swatch as a waste of time. The real waste of time is putting many hours into a garment or other item that you will not be satisfied with. Swatching before beginning your project is like putting a coat of primer on the wall before you begin to paint. It is not a waste of time, rather, it is something you must do if you want to achieve an excellent result.
Bonus: you can unravel the yarn after you swatch, use it in another project, or keep it for an emergency in case you run short of the amount of yarn for your project.