How to Calculate How Much Paint Your Need for a Room

Paint offers a quick, cost-effective upgrade for rooms, but a quality paint job requires forethought for a professional look. Properly estimating the amount of paint needed to finish a room saves you from making extra trips to the store, reducing your time investment. It also eliminates the color variations and streaks caused by purchasing the same paint color in separate batches and applying it at separate times. For the best finish, add a fresh coat of paint to the trim, doors and ceiling as well as the walls, estimating each area separately by the type and color of paint required.

Measure walls quickly with the help of another person.

Step 1

Measure the height and width of each wall and write the measurements down. Multiply the height of each wall by its width to find the square footage and write down your results. Treating each wall as an individual space allows for the most accurate measurements, eliminating discrepancies caused by varying ceiling heights and wainscoting. If ceiling heights are the same throughout, measure the total perimeter of the room and multiply this by the height of the ceiling to find the square footage.

Step 2

Add the square footage of the walls together to find the total paintable square footage.

Step 3

Measure the length and width of the ceiling and multiply the two numbers to find the square footage. Use this same method to find the square footage of doors, crown molding, baseboards and window trim. Write your results down, separating them by area.

Step 4

Read the paint manufacturer's guidelines indicating the coverage level of the paint for each type of paint you're using, including products for walls, trim and the ceiling. The average gallon of paint covers 350 to 450 square feet; however, bare, heavily patched and textured walls soak up more paint, reducing coverage.

Step 5

Divide the paintable square footage of each part of the room by the coverage level of the paint to determine how many gallons you need. Multiply this by the desired number of coats. One coat of primer and two coats of paint covers most surfaces adequately, but you may need a third coat when refinishing stained walls or surfaces previously painted a dark color.