What you do is talk to a bank or mortgage broker or credit union etc. Then you ask them to prequalify you for a mortgage. They'll do credit checks, check your salary and all and give you a number (let's say $200,000). Then they give you a nice letter with "you've qualified for a mortgage of up to x amount". It will also say it's valid for like 60-90 days. Then you know how much to shop for when you're buying a house.
A little warning though, don't take the max of your preapproval. YOu'll set yourself up for bankruptcy. Make sure you calculate your mortgage payments at different mortgage amounts and see what's affordable for you. So if you qualify for $200,000 mortgage, you realistically may only be able to afford a $160,000 mortgage.