6 stitches = 4 inches (10cm) in stockinette stitch worked in the round (knit every round). Be sure to check your gauge.
Knit 2, purl 2 rib (worked in the round, multiple of 4 stitches)
Round 1: *knit 2, purl 2: repeat from * around.
Repeat round 1 for knit 2, purl 2 rib worked in the round.
Finished circumference: about 30 inches (76cm)
Finished height: about 14 inches (35.5cm)