Usually a mortgage lender will approve a mortgage for 4 times your income so if you make say $30,000.00 per year then the bank may be willing to lend you and approve you for a mortgage of $120,000.00
But it's always best to make sure that you can afford the monthly mortgage payments, insurance etc before getting the approved amount for the mortgage.
It's best to get a mortgage less than you can afford if you can so that you won't be house poor.