Here's one plan for knitting a disk: Start with 8 stitches in the first round. Assuming equal stitch heights, the circumference of the second round is roughly twice that of the first round so make one stitch into two stitches, i.e. increase every stitch.
This approach entails beginning with 8 stitches in the first round. Given equal stitch heights, the circumference of the second round is approximately double that of the first round, so combine each stitch into two stitches, thereby increasing the total number of stitches.