How much paint do I need for a 12x12 room?

A 12x12 room with 8-foot ceilings has about 384 sq ft of wall space. Subtracting a standard door (20 sq ft) and window (15 sq ft), the paintable area is about 349 sq ft. At 400 sq ft per gallon, you need about 1 gallon for one coat or 2 gallons for two coats.

How many square feet does a gallon of paint cover?

A standard gallon of interior latex paint covers approximately 350-400 square feet per coat on smooth surfaces. Textured or rough surfaces may reduce coverage to 200-300 sq ft per gallon. This calculator uses the industry standard of 400 sq ft per gallon.

Do I need one coat or two coats of paint?

Two coats are recommended for the best coverage, especially when changing colors or covering dark walls. One coat may suffice for touch-ups or when applying the same color. Always apply primer first when painting over a drastically different color or over new drywall.

Should I subtract doors and windows from the paint area?

Yes, you should subtract the area of doors and windows since you will not paint those surfaces. A standard door is about 20 sq ft and a standard window about 15 sq ft. This calculator automatically deducts them for a more accurate estimate.

Free Paint Calculator — Gallons for Any Room

Paint Calculator

Calculate how many gallons of paint you need for any room, accounting for doors and windows.

Unit

Room Length

Room Width

Wall Height

Number of Doors

~20 sq ft each (standard)

Number of Windows

~15 sq ft each (standard)

Number of Coats

Gallons Needed

Total Wall Area 0 sq ft Doors + Windows Area 0 sq ft Paintable Area 0 sq ft For 1 Coat 0 gallons For 2 Coats 0 gallons

How to Calculate Paint for a Room

Estimating the right amount of paint prevents costly trips back to the store and reduces waste. This calculator determines the total wall area of your room, subtracts non-paintable surfaces like doors and windows, and tells you exactly how many gallons to purchase based on standard paint coverage rates.

The Wall Area Formula

Total wall area is calculated as the room perimeter (2 times length plus 2 times width) multiplied by the wall height. Standard doors are estimated at 20 square feet each and windows at 15 square feet each. The paintable area is the total wall area minus the combined door and window areas.

Coverage and Coats

A standard gallon of interior latex paint covers approximately 400 square feet on a smooth surface. Most painting projects require two coats for even color and full coverage, especially when changing colors. The calculator rounds up to whole gallons since partial gallons are not practical to purchase.

If your walls have a rough or textured finish, coverage may drop to 200-300 square feet per gallon. When in doubt, buy an extra gallon for touch-ups. Leftover paint can be stored for years and used for small repairs. Always purchase all paint at once to ensure consistent color across the room.

Paint Coverage by Surface Type

Surface Type	Coverage per Gallon	Recommended Coats	Notes
Smooth drywall	350-400 sq ft	2 coats	Best coverage; prime new drywall first
Textured walls	200-300 sq ft	2 coats	Texture absorbs more paint
Bare wood / trim	300-350 sq ft	2 coats + primer	Sand between coats for smooth finish
Brick / masonry	150-200 sq ft	2 coats + primer	Porous surface; use masonry primer
Stucco	150-250 sq ft	2 coats	Rough surface reduces coverage
Previously painted (good condition)	350-400 sq ft	1-2 coats	Similar color may need only 1 coat

Paint Calculator

How to Calculate Paint for a Room

The Wall Area Formula

Coverage and Coats

Paint Coverage by Surface Type

Frequently Asked Questions

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