This journey of the why and how of a swatch has been an interesting one, to say the least. I’ve quickly learned not everyone believes in them, while others wouldn’t think to start a garment project without one.
The basis of what I’ve come to understand is that a gauge swatch is crucial in showing how many stitches, and rows, there will be in each inch of the fabric you knit. And that from this knowledge, you can see what is needed to make the garment a certain width or length. Even if you’re following a pattern, a gauge swatch will show if your knitting style, or choice of needles and yarn, will recreate the garment to the size the pattern says it will.
I actually had to laugh at myself as I created one of my first swatches, seen below. It was fascinating to watch my predictions, on how many stitches and rows a particular yarn weight and needle size would need for a 4×4, fall completely apart. Thanks to the always helpful Principles of Knitting, however, I was able to find a formula to remedy my next swatch:
Estimated stitch gauge x width of swatch = approximate number of stitches to cast on
Estimated row gauge x length of swatch = approximate number of rows to work
As I began knitting my next swatch I learned, from accommodating co-workers Beth, Melinda and Annette, why it was so important to make the swatch a square 4-8 inches; namely, the ‘true size’ would be found right smack in the middle of the swatch, meaning a smaller swatch would skew the measurement.
I also discovered that to prevent curling, it’s best to knit four rows at the bottom and top of the swatch, and for every row that is purled, knit three or four stitches at the beginning and end of each row. This not only prevents curling, but also gives cute little edges to the side of this thing that we don’t really wish to be making. 
My next lesson taught me dressing the swatch doesn’t mean I put a skirt on it. Instead, it refers to the process that reveals what your fabric and knit work will look like after it has been washed. You should first check your yarn to be sure of its washability, and if the coast is clear, fill a bowl with lukewarm water and a touch of detergent. Swish the swatch around in the water, then let it settle and soak for about 5 minutes.
Removing the swatch from the bowl, gently squeeze the water out (don’t wring it out!), and place it on a clean towel.
Roll up the towel, and stamp on it with your feet, removing those last bits of water.
Next, block the swatch, which will stretch out the fabric, giving an even better idea of what washing the garment will do to it. Simply pin down the corners of the swatch on a blocking board, then let it dry overnight.
As soon as the swatch is ready, use your ruler or measuring tape to measure a 4-inch strip of its center, placing pins at its beginning and end. Do the same for the vertical rows, and count the number of rows in that 4-inch strip. And voila! That pinned area has determined your gauge! Look to see if your gauge matches that of your pattern, and if not, don’t be discouraged – simple adjustments, or perhaps the knitting up of another swatch, will soon give you the correct gauge.
As well as soothing piece of mind that the many hours you are about to spend creating this garment will result in an absolutely gorgeous item. That fits correctly. 
