Gauge: 21sts in 4inches /10cm in stockinette stitch (row gauge is not important in this case)
You will need: DK yarn (up to 120 grams for adult size), knitting needles to obtain the gauge (please make sure you make a gauge swatch!) for knitting in the round, darning needle to weave in the yarn ends.
Please make a gauge swatch to make sure you match the gauge! The needle size will vary from yarn to yarn and from knitter to knitter! Please check your yarn label to see the needle size the yarn manufacturer recommends to obtain the gauge, make a gauge swatch and adjust the needle size if needed.
Regarding the sizing: the scarf is stretchy; yet the cast on and bind off edge has to be stretchy enough to go over the wearer’s head. It will fit most of those who are in their according age/size.