I Hate Gauge - Or Why I'm Frogging the Back of Mariah

I am apparently completely unable to accurately determine my knitting gauge from my test swatches. Thought I was close with the first toddler sweater (yes, it still sits waiting for that sleeve fix), no, I was way off and wound up with a sweater for a 7 year old instead of a 2 year old.

Then Mariah comes along. I make my swatch, am much more careful this time (or so I thought), and determine that I'm a little off gauge. That's ok because I calculate that their gauge times the max stitches across the back gives a back that is 18.2" across (5 sts/in and 91 sts) and my gauge times the max stitches across the back gives a back that is 19.2" across (4.75 sts/in and 91 sts). So my sweater will have an extra 2" of ease compared to their finished small.

I was fine with this. It's a slightly thicker yarn (I get cold easily) and the extra room gives me space for layering. So I'm all ready to create my new sweater. Knit, knit, knit away happily and all seems well, until I reach a point where I'm far enough away from the ribbing to notice that the sweater seems a little wide. Taking out the handy dandy tape measure I discover, to my serious dismay, that my sweater is not the planned 19.2" across but, rather, 22.5" across!!! So my gauge is actually 4 sts/inch. There is a big difference between 4 and 4.75.

So now I sit pondering how it is that my gauge calculations could be so far off. The sleeves came out to the right size (other than the length issue, which maybe should have been a clue). To make matters even more irritating, I get out my little ruler and check the gauge on the way too big sweater, and it's still looking like 4.75 sts/inch to me. Even though the width obviously proves I'm wrong. I need a major gauge reading tutorial.

Too sad to frog out what I had done I simply pulled it off the needles and put it in the closet. I picked up a new ball of yarn and started over, with many fewer stitches this time around. Let's see if this works. If it comes out the right size I'll just keep going. Otherwise I'll frog the big one back to the ribbing (which fits fine due to the wonders of ribbing) and start decreasing every row until it's the right size.

Keep your fingers crossed for me, it's going to be a long weekend.