Are you asking about space needed to brood the chicks until they are moved out into the coop or how much space, permanently, you would need to house the birds as adults? If the former, are there other birds out in the coop that the young birds would need to be integrated with, is the coop wired with electric, etc. -- these factors will play into how long your chicks might need to be (if at all) in a separate brooder setup vs. in the coop. If the latter, are you certain that you will not exceed 10 birds at any given time, are you planning to free range for a good part of the day or will the birds be confined in the coop/run at all times, what breed(s) are you considering, etc?
There are no magic numbers for either situation - but there are some guidelines that can be used to keep you out of trouble for the most part. My best advice would be don't look at it as a minimum amount of space type thing - "how many birds can I put in x amount of space" - but rather look at it as "how much space can I afford to give over to my flock" and remember that the more space per bird the better.