Gauge for hat, mittens and cowl are stated in the pattern.

You will need circular needles 16 inches long for both the hat and cowl. Also you will need the same size dpns for the hat as the circular needles.

The pattern is worked over a specific number of stitches, so if you need something larger, go up one needle size.

The hat measures 21 inches unstretched.
The mittens measure 8 inches around the knuckles unstretched.
The cowl measures 22 inches unstretched.