Crochet hats

[gemlovesjasper]

When you crochet hats, how do you know how many to crochet in foundation row? I saw a pattern that said to crochet 55. I did and that seemed ridiculously wide. I just want to crochet adult x large. There are two numbers...the head circumference and the hat circumference. I am confused. Which one do I use to make my foundation chain. 

[Granny Square]

Impossible to answer, and a number that works for my stitch gauge may not work with your stitch gauge.  Even if every human on the planet had the same stitch gauge, there are still too many variables.  What size hook and yarn? for whom is the hat intended (Big Man, tiny baby...?) 

Foundation chain?  Not impossible but I'd say unusual; I both knit and crochet, and it seems most knit hats are brim up, and most crochet hats are top down.  I think you'll have to do a lot of looking to find a brim up crochet hat.

http://www.bevscountrycottage.com/size-chart.html  This site gives sizes for average head sizes for babies to grownups, (including adult large that you were looking for), so should prove helpful.

Here is a pattern (free) where they've done the math for you for a basic hat in a lot of sizes.  

 

[bgs]

There are many factors to consider starting with the yarn used. 

https://www.crochet365knittoo.com/yarn-weights-chart/

The size hook used and your personal gauge also factors in.  

This explains sizing hats and the math using your gauge to determine how many stitches you need depending on your gauge to come up with a certain circumference.  

https://oombawkadesigncrochet.com/2018/06/crochet-hat-sizes-and-heights.html