Interior paint calculator

Calculator to estimate how much interior paint to buy for the project.

Input parameters
Room dimensions
Room 1
Room 2
Room 3
Room 4
Room width W1
Room length L2
Ceiling height H3
Substractions on walls (ft2)4
Paint properties5
Wall paint
coverage (ft2/gallon)
# of coats
Ceiling paint
coverage (ft2/gallon)
# of coats

Computed parameters
Total paintable walls area6
Sq. Ft.
Total paintable ceiling area7
Sq. Ft.
Gallons of paint to buy for painting interior walls8
Gallons of ceiling paint to buy9

Interior paint calculator estimates total paintable area and gallons of wall and ceiling paint to purchase for performing painting project based on room size, ceiling height, paint coverage (as stated by manufacturer) and number of coats to apply. Amount of paint to buy for painting doors, windows and trims should be estimated separately.

By default, calculator computes parameters for up to four rooms including painting medium size bedroom with standard window and single door, bigger living room with larger walkway opening in the wall, average in-home office and typical master bedroom. All input parameters can be adjusted based on exact room measurements, paint coverage and necessary number of paint application.

Input parameters

1 W – width of room in feet. Inches values should be entered as real number means 3 inches = 0.25 feet; 6” = 0.5’; 9” = 0.75’ and so on.

2 L – length of room in feet. Input real numbers only.

3 H – ceiling height in feet or distance between subfloor and ceiling joists excluding thickness of gypsum panels and flooring.

4 In subtractions should be included all doors, windows, and other not paintable openings. For example for each 32x80 pre-hung door you must subtract 17 ft2, for each 28x54 window subtract 10 ft2 and so on.

5 Every paint manufacturer provides average coverage of particular paint in square feet per gallon. But actual paint consumption not solely depends on type and quality of paint. Method of paint application, type of paint roller, pile depth of roller cover, condition of surface and who will complete the project will affect actual usage of paint.

Number of coats depends on surface condition at a first place. Normally primed walls should be pained twice for the best results. Application of a single paint coat on primed ceiling typically sufficient in majority of cases.

Adding 10% for waste is typical for performing basic interior painting projects. Under ideal conditions experienced painter could reduce interior paint waste to 5%. During complex custom projects waste factor could be greatly increased.

Computed parameters

6 Total walls area which should be painted excluding all subtractions.

7 Total ceiling area which should be painted in square feet.

8 Amount of flat, eggshell, or gloss paint to purchase estimated based on simple wall paint application using quality 9 in. x 3/8 in. high density woven roller and cutting edges with 3 in. wide angular brush.

9 Amount of ceiling paint to buy calculated based on simple paint application on flat ceilings using polyester roller with 0.375 in. nap and 3 in. wide brush.

Interior paint calculator is for a general purpose only and computes parameters with high accuracy for basic projects. While painting multileveled, tray, coved, cathedral ceiling, arches or custom designed walls consumption of paint will increase significantly. In addition, always take into account the fact: experienced painter, who uses quality paint and tools, might significantly reduce paint consumption and still get better results compare to homeowners who bought cheapest products and for whom painting is a first time home improvement project.