Easiest way is to figure out how much hp you gain from sta is to get a 1 sta aug, put it on, and see the difference it make in your hp. Or, if you arent very lazy like me, just find an item youre wearing with sta and take it off.
Example, say you have 1000hp unbuffed, and you have an item on with 50hp and 5 sta. You take it off and you now have 925hp. So, you lose 50 raw hp, and you lose 25hp from sta. Therefore youre gaining 5hp per 1 sta. Just switch out the numbers or whatever for your hp and the item, its also easier if the item has sta but no raw hp.