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.
Repainting is key to maintaining exterior house paint. The material that your home is made of affects how often you should repaint. For instance, wood-paneled homes need to be repainted twice as often as those made of stucco. Environmental factors also play a role in how often you should repaint, since harsh climates can be hard on a home. As a general rule of thumb, homeowners should repaint their home every six to ten years.
One of the most common home-improvement projects can also be one of the most enjoyable for the entire household. While some aspects of interior room painting, such as masking and “cutting in,” can require some experience and skill, applying a fresh coat of paint to a ceiling or wall or doorway is often a matter of a good brush, a paint tray, and some sweat equity. A coat of fresh paint may be all that’s required to revive a living space that’s faded a bit.

Scale has one of the biggest impacts on deciding whether to hire painting help or take matters into your own hands. If you want to paint your home, consider whether or not this is a realistic task to take on yourself. For instance, is your house multiple stories or a townhouse? Do you just want to paint the kitchen or the entire exterior? Once you factor in the time it takes to do the prep work and lay down multiple coats of paint, a DIY paint job can get complicated. If the house painting job is extensive, you may want to leave it to professionals.
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After you have done the multiplication, subtract about 40 sq feet per window, and about 60 sq feet per door. Divide by 400 (interior paint covers 400 sq feet per gallon). The number that remains, is how many gallons you will need. If doing multiple wall colors, then you should do this process for each room (or sets of rooms) with a particular color. 
Prime. Dark colors, stains (once sealed), and previously unpainted surfaces (drywall, spackle, etc.) will need a primer coat, usually white. NOTE: most paint stores & home improvement centers will now tint primer (at no charge) to match fairly close to the color of the finished coat, that way two coats of primer need not be applied.[6] Although not all surfaces need a prime coat, skip this step at your peril! Dark colors will likely show through the first -- or even the first couple-- topcoats of paint. Sealants and unpainted surfaces like spackle patches will absorb or repel moisture in a topcoat at a different level than the areas surrounding them. Applying a good primer coat will help even out these differences. Primer equalizes a wall to a uniform surface. It's like erasing a canvas before drawing a new picture. Although some will argue the point, you generally don't need to spend a great deal on primer or buy special primer. A cheap, 5 gallon (18.9 L) bucket of plain, flat white paint will usually do the trick and cover a large area. Give your primer at least 24 hours to dry (follow its instructions) before applying a topcoat.
On average, expect to pay $0.60–$1.60 per square foot for exterior painting. The average for painting labor across the country is $30–$40 per hour before you pay for paint, painting supplies, location costs, and equipment. To get a very general estimate, though, painting contractors will take into account the square footage of your home and the number of stories and also factor in normal prep work.
Priming - $30–$40/hour for labor. Many of the materials above need to be primed, but not all do. If you’re changing paint colors from dark to light or light to dark, use a color similar to the top coat. That way you’re less likely to need extra coats over the standard two. Prime with a flat or eggshell paint. You can ask your paint store to add tint to the primer to match it with the top coat color. Hammer in exposed nails and spray them with a metal primer to prevent rust.
In addition to working on our house, Rome has now done jobs for my in-laws, brother, cousin and even a family friend (so its fair to say that I've seen a variety of his work in person) and all of us have been more than pleased with the finished products! If you're browsing for someone to "get the job done", end your search NOW and give Rome a call, you won't regret it!
When determining the total cost of a home’s exterior project, you’ll want to include things like the trim, a garage, foundation, windows and doors. All work is calculated by square footage and sometimes by the linear foot, such as in the case of trim. Your contractor will give you a price for the entire project unless you specifically ask for each item separately.