Most interior paints cover 350-400 square feet per gallon on smooth, primed surfaces. A standard 12×12 room (walls only) requires approximately 1.5-2 gallons for two coats.
📊 Coverage Rates by Surface Type
Smooth Drywall
Textured Walls
Bare/Unprimed Drywall
Previously Painted (Same Color)
🏭 Manufacturer Coverage Specifications
| Brand | Product Line | Stated Coverage | Real-World |
|---|---|---|---|
| Sherwin-Williams | ProMar 200 | 350-400 sq ft/gal | 325-375 sq ft/gal |
| Benjamin Moore | Regal Select | 400-450 sq ft/gal | 350-400 sq ft/gal |
| Behr | Premium Plus | 350-400 sq ft/gal | 300-350 sq ft/gal |
| PPG | Manor Hall | 350-450 sq ft/gal | 325-375 sq ft/gal |
| Valspar | Signature | 350-400 sq ft/gal | 300-350 sq ft/gal |
📐 Paint Needed by Room Size
| Room Size | Wall Area (8' ceiling) | 1 Coat | 2 Coats |
|---|---|---|---|
| 10×10 bedroom | 288 sq ft | 0.75 gallon | 1.5 gallons |
| 12×12 bedroom | 352 sq ft | 1 gallon | 2 gallons |
| 15×15 living room | 456 sq ft | 1.25 gallons | 2.5 gallons |
| 20×20 open concept | 608 sq ft | 1.75 gallons | 3.5 gallons |
| Ceiling (12×12) | 144 sq ft | 0.5 gallon | 1 gallon |
🎨 Primer vs Paint Coverage
Primer Coverage
Paint & Primer in One
⚙️ Factors That Reduce Coverage
Application Method
Roller: 10% waste. Brush: 15% waste. Sprayer: 25-35% waste due to overspray.
Surface Porosity
Unsealed drywall, concrete, and masonry absorb 20-40% more paint than sealed surfaces.
Color Change Severity
Dark to light colors may require 3+ coats. Similar colors achieve one-coat coverage.
Paint Sheen
Flat/matte: best coverage (400+ sq ft/gal). Semi-gloss/gloss: reduced coverage (300-350 sq ft/gal).
Temperature & Humidity
Paint spreads better at 50-85°F. High heat causes faster drying and reduced spread.
📋 Professional Painting Standards
PCA (formerly PDCA)
Two coats minimum on all new or color-change projects
Prime bare drywall with dedicated primer, not paint-primer combos
10% material overage is standard practice for waste and touch-ups
Deduct 20 sq ft per door and 15 sq ft per window when calculating wall area
Common Mistakes
Using manufacturer's max coverage instead of realistic 325-375 sq ft/gal
Skipping primer on bare drywall, stains, or dark-to-light changes
Not accounting for texture which reduces coverage by 15-30%
Underestimating coats needed for dramatic color changes
🔢 Manual Calculation Method
Step-by-Step Example: 12×15 Room (8' Ceiling)
Step 1: Calculate wall area
Perimeter = (12 + 15 + 12 + 15) = 54 feet
Wall area = 54 × 8 = 432 sq ft
Step 2: Deduct openings
Door: 20 sq ft
Windows (2): 30 sq ft
Net area = 432 - 51 = 381 sq ft
Step 3: Calculate gallons needed
Per coat = 381 ÷ 350 = 1.09 gallons
Two coats = 1.09 × 2 = 2.18 gallons
Buy: 2.5 gallons (includes 10% overage)
Quick Formulas
Wall area = (Length + Width) × 2 × Height
Ceiling area = Length × Width
Gallons = Total sq ft ÷ 350 ÷ Number of coats
📚 Industry Standards & Sources
Painting and Decorating Contractors of America (PDCA)
Professional standards for residential and commercial painting. Recommends 350 sq ft/gallon as realistic coverage rate.
Manufacturer Technical Data Sheets
Sherwin-Williams, Benjamin Moore, PPG, and Behr publish coverage rates based on laboratory testing on sealed surfaces.
Master Painters Institute (MPI)
Independent testing organization. MPI standards specify coverage rates, hiding power, and application specifications.
ASTM D344 - Standard Test Method
Industry standard test for measuring hiding power and coverage. Determines paint opacity and spreading rate.