Paint Calculator — How Much Paint Do I Need?
Calculate the exact gallons of paint needed for any room. Includes ceiling, multiple coats, surface condition adjustments, and primer requirements for new drywall.
How to Use This Calculator
- Enter your room dimensions and ceiling height
- Choose whether to include the ceiling
- Enter the number of doors and windows to deduct
- Select number of coats and surface condition
- Click "Calculate Paint" to see gallons needed and primer requirements
How the Calculation Works
wall_area = 2 × (length + width) × ceiling_height
wall_area -= (num_doors × 21) + (num_windows × 15)
ceiling_area = (include_ceiling) ? length × width : 0
total_area = wall_area + ceiling_area
// Coverage per gallon by surface:
// Smooth: 350 sqft | Textured: 300 sqft | New drywall (primed): 300 sqft | Unpainted: 250 sqft
gallons_per_coat = total_area / coverage_per_gallon
total_paint_gallons = gallons_per_coat × num_coats
primer_gallons = surface_needs_primer ? gallons_per_coat : 0 Wall area is calculated from room perimeter × ceiling height with door and window deductions. Coverage per gallon varies by surface condition — new or porous surfaces require more paint. Multiply by number of coats. Primer is recommended for new drywall and bare unpainted surfaces.
Variables:
- total_area: Net paintable area after deducting doors and windows
- coverage_per_gallon: Sqft per gallon depending on surface condition
- gallons_per_coat: Paint needed for one complete coat
- total_paint_gallons: Total paint across all coats
- primer_gallons: Primer needed for new or bare surfaces
Pro Tips
- New drywall is extremely porous — always prime first or use paint+primer for first coat
- One gallon covers 350 sqft on smooth surfaces — textured walls can reduce this to 250–300 sqft
- Two coats are standard for most color changes; dark to light colors may require 3 coats
- Buy primer and paint from the same manufacturer for best adhesion and coverage
- Flat paint hides imperfections well; eggshell or satin is easier to clean in kitchens and hallways
Recommended Products
Frequently Asked Questions
How much paint do I need for a 12×12 room?
A 12×12 room with 8ft ceilings, one door, and two windows has roughly 296 sqft of wall area. At 350 sqft/gallon × 2 coats = 1.7 gallons. Round up to 2 gallons. Plus ceiling (144 sqft) = another half gallon = 2.5 gallons total.
Do I need primer before painting?
Yes if: painting new drywall (even primed drywall benefits from PVA primer), covering dark colors, painting over glossy surfaces, or painting bare wood. No primer needed for repainting existing painted walls in similar colors.
How many coats of paint do I need?
Two coats are standard for most repaints and color changes. Three coats when going from dark to very light colors. One coat may work for minor color changes with high-quality paint+primer products.
What is the difference between flat, eggshell, and satin paint?
Flat: no sheen, best for hiding imperfections, use in low-traffic areas. Eggshell: slight sheen, washable, good for bedrooms. Satin: more sheen, very washable, ideal for kitchens, bathrooms, hallways. Semi-gloss: high sheen, moisture resistant, use for trim and doors.
How long does a gallon of paint last?
A gallon covers 350–400 sqft on smooth surfaces in one coat. For a typical bedroom, one gallon covers the walls in one coat. Most room repaints (2 coats) require 2–3 gallons.