It's important for a painter to gather cost estimates before beginning a painting project. With exterior commercial painting, a professional painter needs to calculate all the costs involved to complete the project such as equipment, materials, labor and other items that may be necessary. Estimates should not be set in stone as modifications could be required and increase the cost of the job, and customers may not be willing to pay additional costs of which they were unaware.
When you're attempting to figure out the total size of the area to be painted in order to determine how much paint you'll need, multiply the width and height of each of the outside walls and add them together for the entire square footage. The square footage of any areas such as windows and doors that will not be painted are subtracted from the total square footage.
For example, to calculate the cost of painting a commercial building that has 40-feet wide x 30-feet high exterior walls, add the four walls for total square footage of 4,800 (4x40x30). The building has eight 6-feet wide x 7-feet high windows (8x6x7=336 square feet) and one 7-feet wide x 9-feet high exterior door (7x9=63 square feet) which you subtract from the total: 4,800 - 399 = 4, 401 square feet needs painting.
Typically one gallon of paint will cover approximately 400 square feet if the walls are smooth and about 300 square feet if the walls are textured. If two coats are needed, remember to account for double the amount of paint. Don't forget to include the costs of paint trays, rollers, drop cloths and brushes. According to the square footage measurements in the project example of 4,401 square feet, you would need approximately 11.5 gallons for a smooth surface and 15 gallons for a textured surface. Most painters prefer premium-quality exterior paint, which costs $25-to-$40 per gallon, so in this case, you need to allow for paint costs between $287.50 and $600.
Labor costs can be calculated by estimating the number of hours it will take to complete the job. If you are hiring help, you will have to factor their hourly rate into the cost of the job. Don't forget to include tasks like wall preparation, caulking, scraping, washing, applying primer, treating problem areas and clean-up when the job is complete. Consider how many hours the job should take and then multiply that by your hourly cost of labor. If you work by yourself, multiply the hours by your regular hourly rate.