Interior painting is one of the easiest trades to underbid. The paint is cheap; the labor is most of the cost, and the square footage is bigger than it looks once you count the coats.
Interior painting looks simple to estimate and is one of the easiest trades to underbid. The paint is cheap; the labor is most of the cost, and the square footage is bigger than it looks once you count the coats. Here is how to estimate a painting job so the bid covers the hours you will actually spend.
Measure the paintable area, not the floor
The number that drives a paint estimate is paintable surface area, and it is almost always larger than the room's floor. For walls, take the perimeter of the room and multiply by the ceiling height. A 12-by-14 room with 9-foot ceilings has a 52-foot perimeter, so roughly 468 square feet of wall before you deduct anything.
Then subtract the openings, the doors and large windows you are not painting, so you are not buying paint and selling labor for surfaces that are not there. Add ceiling area separately if the ceilings are in scope. The result is your true paintable area.
Multiply by coats, then size the paint
Here is the step that gets skipped: paintable area times the number of coats. Two coats on 468 square feet of wall is 936 square feet of actual painting, and that is what both your paint quantity and your labor hours should be based on.
Size the paint from coverage. A gallon covers roughly 350 square feet per coat on smooth, primed drywall, less on rough or porous surfaces. Divide your total painting area by the coverage and round up to whole gallons, then add primer where bare drywall, patches, or color changes call for it. Sundries, tape, plastic, brushes, roller covers, and caulk, are a small but real line; do not let them disappear into the truck.
Price labor by a production rate
Painting labor is best estimated by production rate, square feet painted per hour including cut-in. A painter rolling open walls might run 200 square feet an hour; heavy cut-in, trim, tight rooms, or detailed work drag that down hard. Divide your total painting area by the rate to get hours, then multiply by your burdened labor rate, wage plus taxes, insurance, and overhead on the labor, not the bare wage.
Trim, doors, and cabinets do not follow the wall rate at all; they are slow, detailed work and are usually priced per piece or per linear foot. If a job is trim-heavy, estimating it at a wall production rate will bury you.
Carry overhead and set the markup
Materials plus labor is your cost, not your price. Add the overhead the job has to carry, then your markup, and look at the resulting margin before you send it. A bid that only profits if the crew hits a perfect production rate every day is not really profitable; it is hopeful.
Bid it the same way every time
The painters who quote quickly and accurately have their coverage, production rates, and unit prices saved and just enter the room. The Interior Painting Estimate Template does the takeoff for you, walls and ceilings minus openings times coats, gallons by coverage, labor by production rate, and a bid price with the margin shown, plus a price book for walls, ceilings, doors, and trim at your own rates.
If you run more than paint, the Contractor Estimating & Job-Profit System applies the same approach across trades and prints a client-ready proposal. Both are in the Contractor & Trades tools.
Measure the real area, multiply by coats, price the labor at a production rate you trust, and bid trim separately. That is the difference between a painting job that pays and one that just keeps you busy.