Gauge: 17 sts in stockinette stitch in 4in /10cm (row gauge is not important for this pattern)
You will need yarn (up to 100 grams for the smallest size, up to 200 grams for the largest size), knitting needles to obtain the gauge, a tapestry needle to weave in the yarn ends and a stitch marker.
Since the hat is knit in the round, you will need either double pointed needles or circular needles for magic loop.