A crochet hat for a pet will be a good protection against the vagaries of weather.
Step-by-step instructions, photos and video tutorials will help you crochet a hat quickly and easily.
Pattern provides instructions for S and M size (specific measurements are provided below).
Pattern is provided in 2 versions: US and UK/EU terminology.

Basic crochet stitches used - chain, slip stitch, single crochet, single crochet through the back loop, (US terms).

This pattern contains written instructions with full stitch counts for every row.

S size

Head girth 25 - 27cm / 9⅞ - 10⅝in
Head height 10cm / 3⅞in
Neck circumference 21 - 23 cm / 8¼ - 9in

M size

Head girth 31 - 33cm / 12⅛ - 13in
Head height 12cm /4¾in
Neck circumference 25 - 27cm / 9⅞ - 10⅝in