Interior paint covers 350-400 sq ft per gallon on smooth drywall. Textured walls reduce coverage to 300-350 sq ft/gal. Primers cover 200-300 sq ft/gal. Deduct 20 sq ft per door and 15 sq ft per window.
🎨 Coverage Rates by Surface Type
| Surface Condition | Paint (sq ft/gal) | Primer (sq ft/gal) | Notes |
|---|---|---|---|
| Smooth Drywall (Painted) | 350-400 | 200-300 | Best coverage, similar colors |
| Smooth Drywall (Bare) | 250-300 | 200-300 | First coat absorbs more |
| Textured Walls (Knockdown) | 300-350 | 200-300 | 15-20% more paint needed |
| Textured Walls (Orange Peel) | 300-350 | 200-300 | Moderate texture |
| Popcorn Ceiling | 250-300 | 200-300 | Heavy texture, high absorption |
| Dark to Light Color | 300-350 | 200-300 | May need 3 coats or tinted primer |
Primer Coverage
All primers cover 200-300 square feet per gallon regardless of surface type per PCA standards. This reduced coverage ensures proper sealing, stain blocking, and adhesion for topcoats.
📐 Standard Deductions
Doors
Windows
Large Openings
🧮 Room Calculation Example
12' × 14' Bedroom (8' Ceilings)
Step 1: Calculate wall area
Perimeter: (12 + 14) × 2 = 52 feet
Wall area: 52 × 8 = 416 sq ft
Step 2: Deduct openings
Door: 20 sq ft
Window: 15 sq ft
Paintable walls: 416 - 20 - 15 = 381 sq ft
Step 3: Add ceiling
Ceiling: 12 × 14 = 168 sq ft
Total area: 381 + 168 = 549 sq ft
Step 4: Calculate paint needed
Coverage: 375 sq ft/gal (smooth drywall)
Per coat: 549 ÷ 375 = 1.5 gallons
Two coats: 1.5 × 2 = 3 gallons
With 10% waste: 3 × 1.10 = 3.3 → 1 gallon walls + 3 quarts ceiling
Alternative (walls only):
Walls: 381 ÷ 375 = 1.02 gallons per coat
Two coats with waste: 1.02 × 2 × 1.10 = 2.2 → 1 gallon + 1 quart
🔢 How Many Coats Do You Need?
One Coat Acceptable:
- • Same color refresh (good condition)
- • Light color over light color
- • High-quality paint with primer built-in
- • Previously primed surface
Two Coats Required:
- • New drywall (1 primer + 2 paint)
- • Color change (light to dark or reverse)
- • Stain blocking needed
- • Professional/warranty requirements
Dark to Light Colors
When painting light colors over dark walls, use tinted primer (gray for covering dark colors) plus 2 coats, or plan for 3 coats of paint without tinted primer.
📚 Industry Standards
PCA Standards (formerly PDCA)
The Painting Contractors Association sets coverage standards: 350-400 sq ft/gal for smooth surfaces, 200-300 sq ft/gal for primers. Recommends 10% material overage for waste.
MPI (Master Painters Institute)
Provides architectural paint specifications and performance standards. Defines proper surface preparation, primer requirements, and coating systems for various substrates.
ASTM D3276 - Standard Guide for Painting Inspectors
Establishes qualifications and responsibilities for paint inspectors. Covers film thickness, coverage rates, and quality control procedures.
Manufacturer Specifications
Major brands (Sherwin-Williams, Benjamin Moore, Behr) provide technical data sheets with coverage rates, dry times, and application instructions. Always follow manufacturer guidelines for warranty compliance.
Calculate Your Interior Paint Materials
Calculate paint requirements for walls, ceilings, and trim with surface-specific coverage rates.
Go to Interior Paint Calculator →