How Much Paint Do I Need?
Calculate wall area, account for coats and surface texture, and estimate the gallons of paint required for your room project.
Key Paint Coverage Factors
| Surface Condition | Coverage per Gallon | Notes |
|---|---|---|
| Smooth, previously painted | 350–400 sq ft | Best case on smooth walls; use 350 sq ft/gal for a conservative estimate |
| Bare drywall (unprimed) | 250–300 sq ft | Absorbs more paint; prime first for better coverage |
| Textured or popcorn | 200–250 sq ft | Rough surfaces consume significantly more paint |
| Glossy or eggshell finish | up to 400 sq ft | Smooth surfaces provide better coverage |
How to Calculate Wall Area
- Measure room dimensions: Length and width in feet. Ceiling height in feet.
- Calculate perimeter: Add all four walls' lengths. For a rectangular room: (length + width) × 2.
- Multiply by ceiling height: Perimeter × height = total wall area in square feet.
- Subtract openings (optional): Deduct door and window areas for accuracy. A standard door ≈ 20 sq ft; a typical window ≈ 10–15 sq ft.
Example:
Room: 12 ft × 14 ft, ceiling height 8 ft
Perimeter: (12 + 14) × 2 = 52 ft
Wall area: 52 ft × 8 ft = 416 sq ft
Less 2 doors (20 sq ft each) + 3 windows (10 sq ft each): 416 − 70 = 346 sq ft
For 2 coats: 346 × 2 = 692 sq ft needed
Paint required (smooth surface, 350 sq ft/gal): 692 ÷ 350 ≈ 2.0 gallons → buy 3 gallons
Number of Coats
- Standard project (same color or lighter shade): 2 coats
- Paint-and-primer-in-one product: 2 coats (primer + paint combined)
- Dramatic color change or dark-to-light: 3 coats (primer + 2 paint coats)
- Covering stains or water marks: 2–3 coats depending on the stain
- High-coverage paint brands: May deliver full coverage in 1 coat, but 2 is still recommended for even sheen
Pro Tips for Accurate Estimation
- Always read the label: Manufacturers list coverage rates on the can. Account for the specific surface (drywall, previously painted, semi-gloss, etc.).
- Prepare surfaces first: Clean, prime bare spots, and fill holes. Proper prep reduces the paint needed and improves durability.
- Buy one extra gallon: Extra paint allows for touch-ups later and accounts for measurement variations.
- Test color samples: Paint swatches on walls and observe in natural and artificial light before buying full quantities.
- Account for application method: Roller application typically covers more area than brush. Spray application is most efficient but wastes more paint.
Related Guides
Ready to Calculate?
While this guide covers paint estimation fundamentals, the Tile Calculator at the heart of this site helps with flooring and material projects. For a comprehensive renovation estimate—combining paint, flooring, and tile work—start with your wall and floor measurements and work through each calculator systematically.
Frequently Asked Questions
One gallon of paint typically covers 350–400 square feet on a smooth, previously painted wall with one coat. Bare drywall usually covers 250–300 sq ft per gallon. Textured or popcorn surfaces typically cover 200–250 sq ft per gallon. Always check the product label for the manufacturer's specific coverage estimate.
Multiply the perimeter (length + width + length + width) by the ceiling height, then subtract door and window areas. For example: a 12 ft × 14 ft room with 8 ft ceilings has a perimeter of 52 ft, giving 416 sq ft of wall area before deductions.
Most interior projects need 2 coats for even color and coverage. Primer counts as one coat if using a paint-and-primer product. Dramatic color changes, covering stains, or painting over dark colors may require 3 coats.
Yes, subtract them from your wall area for a more accurate estimate. A standard door is roughly 20 sq ft and a typical window is 10–15 sq ft. Being conservative (not subtracting them) ensures you buy enough paint.
Yes. Rough textures, popcorn ceilings, and unprimed drywall absorb more paint, reducing coverage to 200–250 sq ft per gallon. Glossy or previously painted surfaces have better coverage (up to 400 sq ft per gallon). Adjust your coverage estimate based on the surface condition.