On popular demand I have written the pattern for my Grinch Christmas hat. The hat is soft, warm and very festive !
The pattern is in both USA and UK terminology.

The hat is worked in the round. The red hat on the Grinch is supposed to stand upwards and not fall down to have the effect of the designer.
Yarn
Marriner dc
Chain 80 (adult female)
Make 84 for male
Youngster 72
If you need smaller or bigger sizes - reduce or add by 4 in the foundation chain once you have done the chain and 1 row try if it fits