Don't forget to include your overhead. Figure out the best you can what you'll burn in fuel (I have it calculated what I burn per mile), and then you have insurance, office supplies, advertising budgeting, dump fees, repairs & maintenance, phone, the list goes on. Plus what you want to profit and what you need to make to pay personal bills, personal vehicle, house payment, student loans, credit cards, etc.
When I calculate out my expenses for the upcoming year I prefer it to just know what I have to have per week, per month, and per year, rather than per hour, knowing per hour is very important and I always know what it costs per hour to operate, but I don't always have 40 "billable" hrs in any given week. That's where knowing how much per week or month you must make. For any maintenance work I aim for $75/man hr and hustle hard on the job to get that.