Paint & Primer Coverage Calculator
Calculate gallons, quarts, and primer required for interior walls and ceilings with door/window deductions.
Room Dimensions & Openings
Paint Coverage per Gallon by Surface
The 350 sq ft/gallon standard applies to smooth, primed interior walls. Real-world coverage drops as the surface gets rougher or thirstier.
| Surface / Product | Coverage per Gallon | Notes |
|---|---|---|
| Smooth interior walls (repaint, primed drywall) | 350–400 sq ft | The calculator's default assumption |
| New bare drywall | 300–350 sq ft | Joint compound absorbs more; prime first |
| Textured / rough surfaces (stucco, brick, masonry) | 250–300 sq ft | Texture adds up to 50% more surface area |
| Primer / sealer | 200–300 sq ft | Thicker film designed to block and bond |
| Dark-over-light or bold reds/yellows | 300–350 sq ft | Often needs a tinted gray base coat |
Gallons Needed by Room Size (2 Coats, 8 ft Ceilings)
Assumes one door (−21 sq ft) and one window (−15 sq ft) deducted, 350 sq ft per gallon, two coats of the same color.
| Room | Wall Area | Paint (2 Coats) | Primer (1 Coat) |
|---|---|---|---|
| 10 × 10 bedroom | 284 sq ft | 2 gallons | 1 gallon |
| 12 × 12 bedroom | 348 sq ft | 2 gallons | 1 gallon |
| 12 × 12 (9 ft ceilings) | 396 sq ft | 3 gallons | 2 gallons |
| 15 × 15 living room | 444 sq ft | 3 gallons | 2 gallons |
| 20 × 20 great room | 604 sq ft | 4 gallons | 2 gallons |
Primer rounds up to whole gallons. Add one quart per accent wall or color change, and remember trim and doors are extra — a door plus jamb takes about 1 quart per two coats.
Frequently Asked Questions
How much area does one gallon of paint cover?
One standard gallon of quality interior latex paint covers approximately 350 to 400 square feet with one coat. For rough or textured surfaces (like stucco or bare masonry), coverage drops to 250 to 300 square feet per gallon.
Do I really need 2 coats of paint?
Yes, applying 2 coats of paint provides full color saturation, hides substrate imperfections, and creates a durable, washable film that lasts 2 to 3 times longer than a single thin coat.
How do you calculate paint needed for a room?
Measure the perimeter of the room (Length + Width) × 2, multiply by the ceiling height to find gross wall area, subtract 21 sq ft per door and 15 sq ft per window, multiply by number of coats, and divide by 350 sq ft per gallon.
How many gallons of paint for a 12×12 room?
A 12×12 bedroom with 8-foot ceilings has about 348 sq ft of wall area after deducting one door (21 sq ft) and one window (15 sq ft). Two coats need 696 sq ft of coverage — almost exactly 2 gallons at 350 sq ft per gallon. Buy a quart extra for dark colors or heavily textured walls.
How much area does a quart of paint cover?
One quart covers roughly 87 to 100 square feet with a single coat — a gallon is 4 quarts. That is enough for one door and its trim, a small accent wall section, or touch-ups around a room already painted.