The joys of sizing hats

I struggle with this a lot, I will be the first to admit that. Sizing hats for people can be difficult. But it can be broken down to a way to make it a bit easier.

Now these are generalizations for hat heights. There is some wiggle room for sizing just to account for head size. No babies come out the same size as another baby (my son was a big baby). So if you are making a hat for a baby, just keep in mind. If the hat is a bit too big, they will grow into it, but you can't come back from too small. I personally like to go for a bit on the big side. That way they can wear the hat for a bit longer while they grow and can enjoy it that much longer!

Preemie 1-6 lbs -
Head circumference - 23-33 cm
Hat circumference - 18-28 cm
Hat diameter - 4.5-9 cm
Hat height - 8-11.5 cm

Newborn/baby up to 6 months - 
Head circumference - 33-43 cm
Hat circumference - 30.5-37 cm
Hat diameter - 9-13 cm
Hat height 11.5-16 cm

Baby 6-12 months - 
Head circumference - 40-42 cm
Hat circumference - 36-39.5 cm
Hat diameter - 14-15 cm
Hat height - 16-17 cm

Toddler 1-3 years -
Head circumference - 43-48 cm
Hat circumference - 40.5-46 cm
Hat diameter - 15-16 cm
Hat height - 17.5-19 cm

Child 3-10 years -
Head circumference - 48-51 cm
Hat circumference - 46-48.5 cm
Hat diameter - 16-17 cm
Hat height - 19-20 cm

Teens -
Head circumference - 51-53.5 cm
Hat circumference - 48.5-51 cm
Hat diameter - 17-18 cm
Hat height - 20-22 cm

Adult Woman -
Head circumference - 54-46 cm
Hat circumference - 51-53.5 cm
Hat diameter - 17-19 cm
Hat height - 22-23 cm

Adult Man -
Head circumference - 51-59 cm
Hat circumference - 51-56 cm
Hat diameter - 17-20 cm
Hat height - 22-24 cm