The labour cost to paint anything is the same calculation every time: the hours the work takes multiplied by what an hour of your crew actually costs. What varies, and what published figures cannot know, is the hours, because they come from the surfaces, the number of coats and above all the preparation, which is where most of the time on a repaint goes. Anyone quoting a national figure is quoting an average of jobs that have nothing in common with yours.
How to estimate a paint job by square feet: surfaces, not floor area
Measure walls, ceilings, trim, doors and windows separately, because a door takes far longer per square foot than a wall. A room described by its floor size tells you almost nothing: two twelve by twelve rooms with different trim, different ceiling heights and different conditions are different jobs.
Preparation decides the labor cost to paint interior walls
Filling, sanding, caulking, stain blocking, priming bare substrate and washing. On a sound previously painted wall this is modest; on a neglected one it can exceed the painting. Cabinets are the extreme case: the preparation and the drying time between coats dominate, which is why cabinet work is priced per door and drawer rather than per square foot.
Then apply your own burdened hourly cost, which a painting cost calculator cannot
Wages plus payroll taxes, insurance, holiday and non-productive time. Multiply by the hours and you have cost; apply your margin and you have price. A painting cost calculator that asks only for area is doing one sixth of this and is useful only as a sanity check.
Questions people ask about labor cost to paint a room
What is the labor cost to paint a 12x12 room, and how long does it take?
With sound walls, two coats and modest preparation, most crews work to a figure they know from their own jobs. The honest answer is to time your next three and use that, because condition and trim move it more than size does.
Is the labor cost to paint exterior of house work priced differently?
Yes, because access and preparation dominate and the weather limits when work can happen. An exterior painting cost estimator that ignores access is ignoring the line that most often differs between two quotes.
Why is the labor cost to paint kitchen cabinets so much higher per area?
Because the work is preparation, fine finishing and drying time rather than area. Pricing per door and drawer with the boxes counted separately is the method that produces a defensible number.