The pressure washing business can be competitive, especially with so many contractors bidding on the same jobs. When pricing your services, you want to charge what the job is worth, but you don't want to price yourself out of the market. While it's easier to just charge a flat rate per hour, its not always the most accurate pricing system for pressure washing jobs. In most cases, you will want to actually see the job before you make an estimate, and consider the time, materials and profit margin for each job as well as your local competition.
Decide how much time it will take you. The best way to figure out time estimates is to base it on your prior experience. If you have little prior experience, there will be a learning curve in which you occasionally over- or under-price yourself. But, if you have experience, consider how long it has taken you to pressure wash a similarly sized home, boat, building, etc., and base the current job on what you know from past jobs. Also consider if there are any special circumstances: How dirty is the area to be cleaned? Do you need to ascend to high surfaces or dangerous perches?
Calculate your materials cost. There are two kinds of costs you should calculate when pricing your services: direct and indirect costs. Direct costs include anything that you purchased or will use specifically for that job, like chemicals, gas, disposable gloves and the like. Indirect costs include money spent on items that are used on all jobs, like your pressure washer. Direct costs are much more important when calculating the price on a specific job, but a predetermined base rate covering indirect costs is helpful to factor in on every job.
Figure out your profit. Obviously, you need to make a profit on each job, so you have to factor that in to the overall pricing. This is where the tricky part comes in: walking the line between being competitive and looking out for your own interests. You don't want to rip off your customers, but you also don't want to rip off yourself. How much do you need to add on to the top of each job to make a comfortable living for yourself? What is fair in terms of where you live and the local competition? These are questions only you can answer, so give them adequate thought.
Check out the competition. Before setting a price for your job, see if you can find pricing from other companies that are doing similar jobs in your area. Now, everyone's services are different, and you may take more or less time to do the same job, use higher quality materials, and so on, but looking at the competition lets you know what range you should try to stay in, or risk being priced out of the market.