When you are making your first pressure washing bid, it is important to include as many aspects of the job into your quote as possible. How many square feet you will wash is not the only cost to factor into the quote. As you become more experienced, you will become more accurate in your bidding, and you may not even need to use any formula to help you figure your costs.
Look at the job first. Every job is different. The amount of time you will spend is not necessarily related to the size of the building or object. Consider other factors such as terrain, availability and cost of water, size of ladders needed, how much work must be done off a roof and the accessibility of each part of the building or object to be pressure washed.
Calculate how long the job will take. This determines your hours of labor (including travel time). Mentally walk yourself through doing each part of the job. Count the hours it will take to complete each part of the job. Add the number of hours.
Multiply your hourly rate by the number of hours you project it will take to finish the job. Add in your overhead expenses, such as equipment rental, cost of cleaning solution to remove mold from job surfaces, equipment costs, shop rental (if you have one), utilities for the shop and the amount of fuel you will use if you are using a fuel-powered pressure washer (though you are unlikely to use much fuel overall). Factor in other costs such as a fraction of your yearly advertising expenses, travel costs like fuel and a fraction of your annual vehicle maintenance expenses. You can also use a per-mile figure for calculating your vehicle maintenance costs. Use an online mapping service to help you figure out how much you will drive per job.
Draft a final quote statement, including all of the details of the job you will do. Type it on your computer and print it out on official company letterhead. This helps avoid confusion and mistakes at the end of the job that often occur with verbal quotes. This could occur if the customer forgets the price you told him or pieces of the job you said you would do. Mail, fax, email or deliver the quote in person.
No square or linear footage formula can give you a completely accurate estimate of the time it will take to complete the job.