Paint Calculator
Calculate how many gallons of paint you need for walls and ceilings — with door and window deductions.
Based on 350 sq ft coverage per gallon. Cost estimate assumes $30–$50 per gallon for mid-range interior latex paint.
How It Works
This calculator estimates the gallons of paint needed based on your room dimensions, number of coats, and openings (doors and windows). It deducts ~21 sq ft per door and ~12 sq ft per window from the total wall area.
Formula: Wall Sq Ft = 2 × (Length + Width) × Ceiling Height − (Doors × 21) − (Windows × 12). Gallons = Sq Ft × Coats ÷ 350.
Standard coverage is 350 sq ft per gallon for smooth interior walls. Textured or porous surfaces may require more paint. Results are rounded up to full gallons.
Frequently Asked Questions
How many gallons of paint do I need for a room?
A typical 12×12 room with 8-foot ceilings needs about 1.5 gallons for two coats after subtracting doors and windows. Larger rooms or rooms with vaulted ceilings require more. Use this calculator for an exact estimate based on your room dimensions.
How much area does one gallon of paint cover?
One gallon of interior latex paint covers approximately 350–400 square feet on smooth drywall. Coverage drops to 250–300 sq ft on textured walls, bare wood, or porous surfaces. Always check the manufacturer's label for the specific product you're using.
Do I need to paint two coats?
Two coats are recommended for most interior painting. A single coat may suffice when repainting the same color with high-quality paint and primer-in-one. Two coats ensure even color, better durability, and full coverage — especially when changing colors or painting over dark walls.
Should I subtract doors and windows from my paint calculation?
Yes. A standard interior door is about 21 sq ft and a standard window is about 12 sq ft. Subtracting these openings prevents you from buying too much paint. This calculator automatically deducts doors and windows based on your counts.
How much does it cost to paint a room?
Paint costs $30–$50 per gallon for mid-range interior latex. A 12×12 room typically costs $50–$100 in paint alone for two coats. Add $20–$40 for primer if needed, plus supplies like rollers, brushes, tape, and drop cloths ($30–$60).