One gallon of interior paint covers 350 to 400 sq ft. Calculate surface deductions and wall porosity to order the exact gallons with zero surplus.
The 350 Square Foot Coverage Standard
Under standard professional painting conditions, one gallon of latex or acrylic paint provides 350 square feet of uniform coverage on smooth pre-primed drywall.
However, wall texture impacts coverage significantly: rough textured drywall (such as knockdown, orange peel, or bare masonry) increases surface area and absorbs more paint, reducing effective coverage to 250 to 300 square feet per gallon.
Wall and Opening Deductions
To calculate net wall area for a room measuring 14 ft by 16 ft with 9-foot ceilings:
1. Calculate wall perimeter: (14 + 16) × 2 = 60 linear feet.
2. Calculate gross wall area: 60 ft × 9 ft height = 540 square feet.
3. Deduct doors and windows: Standard doors are 21 sq ft (3×7 ft) and windows average 15 sq ft (3×5 ft). For 1 door and 2 windows: 540 - 21 - 30 = 489 net square feet.
4. Calculate for 2 coats: 489 sq ft × 2 coats = 978 total square feet.
5. Gallons needed: 978 ÷ 350 = 2.79 gallons (Order 3 gallons).
| Room Dimensions (8ft Ceiling) | Net Wall Sq Ft | 1 Coat (Gallons) | 2 Coats (Gallons) | Ceiling Gallons (1 Coat) |
|---|---|---|---|---|
| 10 ft × 12 ft (Small Bedroom) | 300 sq ft | 0.85 gal (1 gal) | 1.71 gal (2 gal) | 120 sq ft (0.5 gal) |
| 14 ft × 16 ft (Master Bedroom) | 430 sq ft | 1.23 gal (2 gal) | 2.46 gal (3 gal) | 224 sq ft (1 gal) |
| 20 ft × 20 ft (Open Living Room) | 570 sq ft | 1.63 gal (2 gal) | 3.26 gal (4 gal) | 400 sq ft (1.5 gal) |
| 8 ft × 10 ft (Bathroom) | 240 sq ft | 0.69 gal (1 gal) | 1.37 gal (2 gal) | 80 sq ft (1 quart) |
When is a Dedicated Primer Coat Required?
While many modern paints advertise "Paint + Primer in One," a dedicated acrylic bonding primer is strictly required when:
• Painting over brand-new unpainted drywall or fresh joint compound mud.
• Transitioning from an existing dark, saturated color to a light pastel or white.
• Painting over glossy oil-based enamel with water-based latex.
• Covering water stains, smoke soot, or wood tannins (use stain-blocking shellac or oil primer).
Frequently Asked Questions & Answers
Click any question below to expand quick answers, formulas, and expert tips.
How many coats of paint do I need on interior walls?
When applying a similar color over an existing coat, 1 high-quality coat may suffice. When changing colors or painting fresh drywall, 2 coats are required for complete opacity and true color fidelity.
How much paint is needed for baseboards and trim?
One quart of trim paint typically covers 80 to 100 linear feet of standard 4-inch baseboards with two coats.
