I see crochet patterns all the time where they have all different sizes from newborn to large adult. And it doesn’t always turn out the right size, with different yarns and tension. But in reality, if you have the recipient (or a similar sized one) nearby there’s a much easier way to size the hat.
Since you are usually starting from the top, you need to start flat – magic circle – and work a flat circle by increasing until you suddenly stop increasing and work down the sides. So when does this happen?
Answer: when the circle is the size of the wearers hand.
As I was making a hat for her cousin who is about a year older, I did another round of increasing and then started down the sides.
The hat is slightly too big for her, as I did the extra row of increasing, so hopefully, it will be perfect for her cousin!!
I hope this helps! Give it a try, pick a favourite stitch and make up your own crochet hat pattern, start with a magic circle, increase by the number of stitches in the magic circle every row until it’s as big as the hand. Good luck, tell me how you went?!
PS. babies heads are a bit disproportionate and you should make sure their hand fits comfortably inside the circle before starting the sides.