Analyze you monthly spending, gas, entertainment, vacations, money set aside etc. Some people spend more, some less for your life style. One you had a handle on that amount, you can decide the amount of monthly payment that's a fit for you for your first home.
A lender can provide that number for you based on a purchase price of a home, your credit score and % down.
Yes, they can give you a percentage but this is not a one size fits all when it comes to our spending habits.