How do I figure paint quantity for a 12x14 room with 9-foot ceilings, two windows and one door, two coats on the walls only?

Quick Calculation (Walls Only, 2 Coats)

1. Wall Area: Perimeter × Height = 2(12+14) × 9 = 468 sq ft
2. Deductions: Standard Door (3'0"×6'8"): ~21 sq ft Two Windows (avg 3'×5'): ~30 sq ft Total Deductions:* ~51 sq ft
3. Net Area (1 coat): 468 - 51 = 417 sq ft
4. Total Area (2 coats): 417 × 2 = 834 sq ft

Paint Needed:

• Coverage: 350–400 sq ft/gal (check can label).
• Gallons Required: 834 ÷ 350 ≈ 2.4 gal → Buy 3 gallons.
• Note: If using a premium paint with 400+ sq ft/gal coverage, 2 gallons + 1 quart might suffice, but 3 gallons ensures touch-up stock.

Pro Tips:

• Substrate: New drywall or drastic color change? Prime first (adds 1 coat). Primer covers ~300–400 sq ft/gal.
• Texture: Heavy orange peel/knockdown reduces coverage 10–15%.
• Application: Rolling uses more paint than spraying; back-rolling spray adds ~20%.
• Waste Factor: Add 10% for roller absorption/trim cutting.

Buy: 3 gallons of finish paint. If unprimed, add 2 gallons of primer.

To calculate paint quantity for a 12' x 14' room with 9' ceilings, two windows, one door, and two coats on walls only:

Step 1: Calculate total wall area Perimeter = 2 × (12 + 14) = 52 ft Wall area = Perimeter × Height = 52 ft × 9 ft = 468 sq ft

Step 2: Subtract openings

• Door: Standard size ≈ 3 ft × 7 ft = 21 sq ft
• Windows: Assume average 3 ft × 4 ft each = 12 sq ft per window → 2 × 12 = 24 sq ft

Total openings = 21 + 24 = 45 sq ft

Step 3: Net paintable wall area 468 sq ft – 45 sq ft = 423 sq ft

Step 4: Account for two coats 423 sq ft × 2 = 846 sq ft total coverage needed

Step 5: Determine paint required Most interior latex paint covers 350–400 sq ft per gallon (check label; use 350 for conservative estimate). 846 ÷ 350 ≈ 2.42 gallons

Recommendation: Buy 3 gallons to ensure full coverage, allow for touch-ups, and account for surface texture or absorption (e.g., new drywall may need more). Round up — never buy partial gallons unless mixing custom colors.

Note: If walls are previously painted and smooth, 2.5 gallons may suffice, but 3 gallons is safer and standard practice for pros. Always stir paint well and use a ⅜"–½" nap roller for textured walls. (Reference: IRC R303.1 for habitable space; paint coverage per manufacturer specs like Sherwin-Williams or Benjamin Moore.)