Paint Calculator
Paint = (area × coats) ÷ 350 sq ft/gal
How Paint Coverage Calculations Work
Paint quantity depends on total paintable surface area and how many coats you plan to apply. Wall area for a rectangular room is: 2 × (length + width) × height. A 12 ft × 12 ft room with 8 ft ceilings has walls totaling 2 × (12 + 12) × 8 = 384 sq ft. Add the ceiling (length × width) if painting overhead: another 144 sq ft for 528 sq ft gross.
Subtract openings — each standard door is about 21 sq ft and each window about 12 sq ft. A room with one door and two windows loses 21 + 24 = 45 sq ft, leaving 483 sq ft paintable. Most interior latex paint covers 350 sq ft per gallon per coat. One coat needs 483 ÷ 350 = 1.38 gallons; two coats need 2.76 gallons — buy 3 gallons.
Coverage varies by surface texture, color change, and paint quality. Rough stucco or dark-over-light transitions may drop coverage to 250–300 sq ft per gallon. Primer is essential when covering stains or bold colors and counts as a separate coat. Semi-gloss and enamel often spread slightly farther than flat finishes on smooth drywall.
Exterior painting adds soffits, fascia, and trim not captured in a simple room calc. Multiply height by perimeter for siding, then add trim and shutter area separately. Spraying uses more paint than brushing (~10–15% more) but saves labor on large jobs. Always stir paint thoroughly and maintain wet edge to avoid lap marks.
| Room | 1 Coat | 2 Coats |
|---|---|---|
| 10×12 ft, 8 ft ceiling | 1.1 gal | 2.2 gal |
| 12×12 ft, 8 ft ceiling | 1.4 gal | 2.8 gal |
| 14×16 ft, 9 ft ceiling | 2.0 gal | 4.0 gal |
| 20×15 ft, 8 ft ceiling | 2.3 gal | 4.6 gal |
Enter room dimensions, door and window counts, ceiling preference, and number of coats to get gallon and liter estimates. Use the drywall calculator alongside this tool when prepping new construction walls.
Examples
| Example | Result |
|---|---|
| 12×12 ft room, 8 ft, 1 door, 2 windows, 2 coats | ~2.8 gallons |
| 10×12 ft bedroom, 8 ft, 1 door, 1 window, 2 coats | ~2.2 gallons |
| 14×16 ft living room, 9 ft, 2 doors, 3 windows, 2 coats | ~4.0 gallons |
| 12×12 ft, ceiling included, 2 coats | ~3.0 gallons |
| 8×10 ft bathroom, 8 ft, 1 door, 1 window, 1 coat | ~1.0 gallon |
| 20×15 ft great room, 10 ft, 2 coats | ~5.5 gallons |
| 10×10 ft office, 8 ft, no openings, 2 coats | ~1.8 gallons |
Frequently asked questions
Most interior latex paints cover about 350 sq ft per gallon per coat on smooth, primed drywall. Textured or porous surfaces reduce coverage.
Two coats are standard for even color and durability, especially when changing colors dramatically or painting over new drywall after primer.
Subtract roughly 21 sq ft per door and 12 sq ft per average window from total wall area. This calculator applies those deductions automatically.