Stop guessing at the paint aisle. This calculator tells you how many gallons of paint to buy for any room, accounting for doors and windows you won't be painting and the number of coats you plan to apply.
Room Dimensions
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Openings & Coats
Scenario: You're painting a 10 ft x 11 ft nursery with 8 ft ceilings. The room has 1 door and 1 window, and you want 2 coats.
Result: Total wall area is 336 sq ft. Subtract 1 door (21 sq ft) and 1 window (15 sq ft) for 300 sq ft of paintable surface. At 2 coats, that's 600 sq ft of coverage. At 350 sq ft per gallon, you need 2 gallons.
With 8 ft ceilings, a 12x12 room has 384 sq ft of wall area. Subtract about 51 sq ft for a door (21 sq ft) and two windows (15 sq ft each), leaving 333 sq ft. For 2 coats, you need about 2 gallons (333 x 2 / 350 = 1.90, rounded up).
One gallon covers about 350 sq ft on smooth surfaces. Textured walls, bare drywall, and dark-to-light color changes may reduce coverage to 250-300 sq ft per gallon. Always check the label on your specific paint.
Use primer on bare drywall, when covering a dark color with a light one, or when switching between oil-based and latex. Many modern paints include primer built in, and those work fine for same-color refreshes. For drastic color changes or stain coverage, a dedicated primer saves you a coat or two of expensive paint.
Yes, always buy a little extra. You'll need touch-up paint for scuffs and nail holes later. Paint colors vary slightly between batches, so touch-up paint should come from the same purchase. An extra quart is usually enough.
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