How do kn how much to charge

What I've been doing is calculating jobs based off of my hourly rate. I've discovered that there's a target sweet spot for the services that I offer for the residential side and for the commercial side. For bigger projects, I typically take my hourly rate and multiply it By how many estimated hours it would take me to do that job, and that's what I'll submit my quotes for. However, I do have fixed prices for other types of jobs. Like, for example, tv mountings, they have a set price. As one of the contributors said, I would get with your accountant to estimate how much it costs for you to operate your business and, I think it would be a good idea to come up with a price book for all the services you offer.