La formulazione delle domande con How più un avverbio o un aggettivo ha una sua collocazione precisa all'interno dell'insegnamento della lingua inglese a livello intermedio.
Ecco alcuni esempi:

How long have you been studying english?
How regurarly do you do your exercises?
How fast is it?
How old are you?
How fast does it travels?
How many guests would you invite to your wedding?
Do you want to have children? If so, how many?
How long do you think couples should know each other before they get married?
How old were your parents when they got married?
How big is your family?
How often do you see your grandparents?
How much does it cost?