I have come up with another method for swatchless knitting.
Debbie New has a few in her book Unexpected Knitting. They include knitting on the bias and adding stitches each side, like knitted dishcloths. At this point, I should say that I am only talking in a theoretical way at this point as I have never knit anything as practical as a dishcloth. This way you knit a piece with a right angle and then when your sides are as long as the shortest side, you start decreasing at the same rate, if you want it to be rectangular, you continue increasing on one side and decrease on the other.
She calls her other method log cabin knitting, and she casts on a few stitches knit a few rows, binds off, and picks up more stitches off one of the sides, knits a few rows, binds off, repeats. This can make a square or I suppose whatever rectangular shape you want, like a log cabin quilt.
I imagine Debbie New as the most fun person in the whole world to have in a knitting group.
Her ideas are great, but I have formulated another way, though it really only works when you design your own patterns.
My method was inspired by Norah Gaughan’s Roundabout Leaf Tank from Knitting Nature. In it, you start with a strip of knitting and knit long enough to go around your hips then you start knitting it together with the beginning of the strip in a spiral making up the body of the sweater.
What I figured, was that you could just cast on some stitches and start knitting without making a swatch, because you could measure your gauge from your first piece and work out your pattern for the whole garment. Then you cast on enough to make the other side of the front or back or enough to do the whole rest of whatever you are are knitting and at the end of your first row, start knitting your new piece together with your first piece.
The stitch I use to knit the two pieces together is as follows: work in pattern to last stitch of RS row, slip 1 with yarn in back, pick up and knit 1 stitch from the first row of other piece, pass slipped stitch over, turn, slip 1 stitch with yarn in front, knit to end. This stitch works when picking up from the left edge of the right side of knitting; I have figured out how to do it on the left edge of the wrong side, but it is more convoluted.
If you would like to knit a design I knit this way, please see my Morse code vest.