The swatch: step one

Here is my swatch. I dunked it in water and walked away. Once fully soaked in water, I rolled it in a towel to absorb as much as possible. Now I am patiently waiting for it to dry. Then I will measure it for my stitches per inch. (SPI)
Then I have to figure out which size in the pattern to use to get the size I want.
Since my pattern calls for a heavier yarn, I have to do some mathematics.

I'll guess that one size larger than I usually wear might work since I am using lighter yarn and smaller needles.

I'll take the number of stitches cast-on for the pattern back and divide it by my number of SPI. that should tell me how wide the back will be with my yarn.