Step One: Measure Your Foot
My sock patterns are all sized by finished sock circumference. Measure at the largest part of your foot. For most of us, this will be the ball of the foot, the cushioned part below where our toes end. Grab a tape measure, wrap it around that part of your foot, and see just how big it is.
Step Two: Make a Gauge Swatch
Use the needles and yarn you plan to use for your actual sock, cast on about 70 stitches, and knit until your swatch is a couple inches long. Once the swatch is blocked and dry, use a measuring tape or gauge finder to figure out how many stitches per inch are in your swatch, and if it matches the stitch gauge of the pattern.
Once you know how big your foot is and have figured out what size needles/yarn you need to use to match my gauge, find a sock size that’s close to it. Look for the sock size that is closest to your foot measurement. If that sock size is larger than your foot measurement, choose the next size down.
Step Three: Check the Dimensions of the Sock Sizes and Do a Little Bit of Math