If you are new to knitting, "gauge" is something you have encountered but possibly not understood. In knitting, gauge refers to the number of stitches per inch. You have probably been informed that correct gauge is critical, that you should check your gauge as you work, and you really should knit a gauge swatch before you get started on the project (as if we gung-ho newbies have any patience or tolerance for perfectly good knitting time wasted on creating a gauge swatch). Your first line of defense is selecting the correct yarn for a project. Where I live, it's rarely possible to locally buy the yarn recommended for a particular pattern. Sometimes, I can find the recommended yarn but prefer something else. The yarn label should give you a gauge range and a recommended needle size. Of course, you still have to make a gauge swatch to be sure. Your tension could be different from the test-knitter's, so you have to check. Still, the label and the right yarn are the best starting points.
What happens when your gauge is off? What if you have too many or too few stitches per inch? If you are still in gauge swatch phase, this is an easy fix: simply change needle size. Use a size up if too many stitches per inch (to make looser stitches/fewer per inch) or use a size down if you have too few stitches per inch (to make your stitches tighter/more per inch). Then again, what if you just plowed ahead, gauge swatch be damned? Well, you will wind up with something like this:
This is the Child's Placket-Neck Pullover in the newborn size...or not. There is not a single error in the knitting. All stitches are present and accounted for, increases and decreases are in the correct spots. Not a stitch has been dropped. The tension is beautiful. AND OFF. That measuring tape reveals that this sweater is a whopping 10" across! I happen to like the feel of this yarn (Jo Sharp's Silkroad DK Tweed) knit on a size-up from recommended. That gives it a gauge of 19 stitches over 4 inches. This pattern requires a gauge of 21 stitches over 4 inches. As I knit, I knew my gauge was off. I figured, "What's a couple of stitches every 4 inches? What harm could it do?" I was so close to being done, and I figured I'd just see how it looked when finished. Then, this afternoon, I met my perfectly tiny and wonderful new neighbor (5 days old! 1st day home!), and when I came home, the first thing I did was rip out this sweater although I was only 10 rows short of completion. There was no way this was ever going to fit a normal baby. Not even close. My beautifully knitted baby sweater is (was) perfectly sized to contain the full belly of a one year old, while the length of torso and arms would fit an average 3 month old. Hmm.
So now I have one big ball (the body) and two little balls of yarn (the sleeves) waiting for a future project. Almost done...but then not at all. Sigh.
For the record, this is not my only misjudged project this week. I did indeed finish the pajamas for my daughter. They are unbelievably cute, but they don't fit. Five years of dressing her in jersey makes correctly-sized garments in stiffer cotton "too tight" and unwearable. Oh well. At least I have another girl who will eventually grow into them. Back to the drawing board!