One important consideration when comparison shopping for interior paint is the manufacturer’s available palette. One brand of latex paint may be significantly less expensive than others, but the tint options can be limited. There can also be a noticeable difference between one manufacturer’s “midnight blue” and another’s “Prussian blue.” There is no universal standard, so this is why sample cards and test paints are so important.
Two aesthetic things to consider when selecting a finish are how shiny you'd like the surface to be and whether or not you want to hide any imperfections on the surface to be painted. Generally, higher-gloss paint finishes reflect light better than lower-gloss finishes, like eggshell and matte. That makes them shiny, and also causes them to highlight flaws in walls and ceilings.
If you have kids, pets, or occupants who will damage the walls, it is recommended to go with washable matte, eggshell, or satin, because these paints can be easily cleaned and are more durable. However, flat paint can be touched up more easily and hides imperfections better, so if you are selling the home, it is highly recommended to go with flat. Bathrooms with showers/tubs should go in semigloss- unless you are selling or want a specific design look, then use satin. 
Determine the coverage area for each color and estimate the number of gallons you'll need for each. For odd walls with angled ceilings, make your best guess. If you're not comfortable doing this, measure the wall at its highest height and multiply that by its width. Now subtract the lowest height from the highest height, multiply that number by the width, cut that answer in half, and finally subtract that new number from the original height by width. That should give you the wall area.
However, some water-based paints are easier to work with than others. The first coat of paint may not provide complete wall coverage, or the color may not be quite as saturated. Some of these problems can be addressed with a separate primer coat, but this is a time-consuming project. The ideal solution is using a higher-quality paint that combines a primer and a finish paint in a “one coat” product.
Remove any outlet covers or lighting fixtures (if possible). Then scrutinize the walls for any defects. Simply fill them in with caulk or spackling compound if you encounter cracks, dents, or holes in your walls and trims. There are also tips and tricks for filling nail holes. Once done with the repair, smoothen the wall down with sandpaper and then wipe it with a damp sponge.
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. 

Paint can be expensive. Buying too much paint is particularly frustrating since paint stores won’t refund an already tinted gallon of paint. That’s why it’s recommended to first buy around 80% of the estimated paint you need and then purchase the remainder when you’re almost finished. Factors such as square footage, surface type, and quality of paint all play into how much paint you’ll need. Paint stores should be able to help you determine how much paint you need for a specific job. If you aren’t sure how much paint to buy, ask a salesperson for advice.
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.
Needless to say, an exterior paint job tends to be more complicated. Indoors, you don’t have to deal with the elements. When painting the exterior of a home, however, you have to think about tough to reach places and the unpredictability of the weather. If you just want to repaint your front door, we trust that you’ll be able to do it yourself. Contrarily, a full exterior makeover requires professional help.
Most of a projects price is the cost of labor at $25 to $75 per hour. However, most contractors bid out based on the entire project which includes all work hours. Hourly rates are only useful if your pro asks to do the job as “time and materials.” However, be wary of this pricing structure, it usually shows the contractor is uncertain how long the project will take.
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