Paint Calculator

Rarely. 'One-coat' claims on the can assume ideal conditions: similar existing color, smooth surface, premium paint, perfect technique. Two coats is the honest default for uniform color and durability — and going from dark to light (or the reverse) may want a tinted primer under those two coats, which is cheaper than a third coat of finish paint.

350 sq ft per gallon is the standard manufacturer figure for smooth, sealed, previously painted walls. Use 250–300 for bare drywall (it drinks paint), textured surfaces, masonry, or strong color changes. The difference is real: a 12×10 room at two coats can swing from 1.5 to 2.5 gallons on coverage alone.

Buy the calculated amount plus a little — but prefer a quart over an extra gallon when you're close. Keep the leftover: touch-up paint from the same batch matches perfectly, while a can mixed months later at the store may be visibly off. Note the color formula from the can lid before recycling it.

Just openings. The standard deductions — about 21 sq ft per door, 15 per average window — approximate what you genuinely won't paint. Painters often skip deductions entirely on rooms with one door and one window and treat the surplus as their waste margin; the calculator deducts them so the waste stays visible and intentional.