While you may choose to paint a door, ground-level window trim and other parts of your house’s exterior, it’s really a job best left to the professionals. One of the main reasons is experience. An experienced painter knows how to handle the prep work, spot problems and identify sources of future trouble, all while getting the job done more efficiently. They are also experienced with spending long hours on tall ladders. If you want high-quality work, it’s best to hire a professional painter near you. 

Prep the house. Wash the walls, remove wallpaper, patch, spackle, seal stains, dry and sand before you attempt to paint. Now is also the time to apply painters tape for trimming, lay drop cloths, etc. Remove all outlet and light switch face plates, collecting screws in a zip-top bag (good opportunity to wash the face plates all at once as well).[4] You can also buy your paint at this time. Don't wait until the last minute. It can take hours to mix many gallons of all your colors. Remember that traffic triples at your home-supply and hardware stores on weekends. Buy on a weekday if possible.
Painting a brand new house with smooth surfaces dramatically reduces prep work. On the other hand, if you’re painting an old home with peeling walls or siding, it’s going to take a lot longer. When deciding whether to hire house painting professionals or do it yourself, take the current state of the paint into consideration. If you’re not up for the challenge of scraping and sanding for hours, you should hire help to get the best results.

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).
An example of the wall measurement would be: 40 linear feet of bedroom space, x 8 wall height, =  320, x 2 = 640. Minus 1 door (60) and 2 windows (80) = 500 sq feet being painted. Then divide the 500 by 400 (sq feet per gallon), and you get 1.25 gallons (4.73 L) needed for that room. For this, you'd need 1 gallon (3.8 L) and 1 US-quart (950 ml). If the amount it comes out to is over 1.3, we recommend just getting 2 gallons (7.6 L) so that you have leftovers if needed, since 2 US quarts (2,000 ml) costs essentially the same as a gallon in most stores.
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: