For walls, measure the linear feet of wall space (measuring along the baseboards) for the areas to be painted (using a tape measure, laser, or both). Then multiply this by the ceiling height (usually it is 7.5 or 8). If there are 2 story areas, measure them separately, and multiply them by double the regular wall height. Then multiply the total number by 2 (for 2 coats).
While some professional painters will charge a flat fee for a painting project, most charge an hourly rate—about $25 to $100 per hour on average. Most painters will charge more for last-minute jobs (think 48 hours' notice or less), travel costs (if you live far away, the painter may want extra money for gas), or intensive prep work (e.g., removing mold or stains before painting). Also, depending on the painter, the rate may or may not include the cost of paint materials such as paint, primer, and supplies.

A single gallon of paint can run anywhere from $20 to $80 per gallon. Professionals get a contractor discount of anywhere from 25 to 50 percent. For rough siding, like stucco, you’ll need to use 10% to 20% more paint. Some textures, like wood and stucco, require extra paint because they have more surface to cover in a tiny area compared to smooth siding. Use the highest quality exterior paint your budget will allow for your project. It will look the nicest and save you money by offering better coverage and durability. Better coverage means fewer coats and fewer work hours. You’ll also go a few years longer without needing to shell out more cash for a new coat. How do you know how much paint you're paying for? Here's some helpful math: