How much does it cost to paint a room? This is a broad question so let's try to narrow the focus and have an upfront discussion.
First, let's settle on the size and type of a room. For simplicity we should stick to a 12' x 14' bedroom that has 2 standard doors, 2 standard windows, and 8' ceilings. With this being stated we know that we have 416 sq/ft of wall space MINUS 42 sq/ft(3'x7' door allowance x2) and 24 sq/ft(3'x4' window allowance x2) which would lead to 350 sq/ft of actual wall space to be painted.
Secondly, we need to decide on whether we are painting ceiling, trim, doors, and/or the inside of the closet. These additional items add time and material which translates into increased cost. A ceiling would add 168 sq/ft of surface to be painted, trim(baseboard only - NO crown molding or chair rail) would add approximately 108 sq/ft of surface to be painted, the interior of a basic(4'x8') closet would add approximately 100 sq/ft to be painted, and 2 slab doors would add 42 sq/ft of surface to be painted.
Thirdly, we need to determine the amount of surface preparation that is needed for the walls, trim, and doors. Are we just patching minor small nail holes, caulking minor cracks, and painting already painted trim? Is there staining on the ceiling, contaminants on the walls, major patching, dark colors to be covered/applied, or natural trim to be painted? Are we moving furniture and wall hangings? Extensive surface preparation adds labor and materials.
Fourthly, we need to determine how many coats of paint are we applying to each specified surface and area that is to be painted? Typically, we subscribe to a singular coat on the ceiling, a single coat in the closet, a minimum of 2 coats on the walls, and 2 coats of paint on the trim. *This is breaking it down to its simplest form and any additional items refers back to the third point of surface preparation. Additional coats of paint add labor and materials.
Fifthly, we need to settle on the areas to be painted, preparation, and product requirements. For this example we will say that we are painting the ceiling, walls, inside of the closet, and NO TRIM. We are just patching minimal nail holes, lightly sanding the walls, and no dramatic color changes. Our square footage for the walls is 700 sq/ft(2 coats of paint - 350x2=700), 168 sq/ft for the ceiling(1 coat of paint), and 100 sq/ft for the inside of the closet(1 coat of paint). We would need AT LEAST 2 gallons of wall paint and AT LEAST 1 gallon of paint to be shared amongst the ceiling and closet.
Next, we get to the product associated with the job. Typically you will spend $35-$50 a gallon for a quality satin/eg-shel wall paint, $25-$35 a gallon for a flat ceiling paint, and need to add 15% for additional products needed for the job. So you have the following in material cost - $90($45x2)+$30($30x1)+$18(.15x$120)=$138 .
Finally, we would get to the labor cost. We are basing this number on our labor costs, overhead, business costs, and profit needed to grow our business. We roughly estimate 2.5 hours of labor for ceiling/closet and 7.5 hours of labor for the walls(this includes moving furniture, wallhangings, and putting back wall plates). So you would have $138 in material cost and $525 in labor cost for a grand total of around $688 in this project example. Again, this is an estimate based on the numbers, not speaking with a client, not seeing a job in person, and for educational purposes.
* It is important to set the parameters and clarify the scope of the job up front in order minimize confusion, allow for proper job estimation, and set expectations. The labor cost is dependent the individual businesses operational costs, acceptable profit margin, and hidden costs(such as insurance, payroll costs, benefits, and more).