Paint Calculator
Calculate how much paint you need for any room. Get total wall area, minus doors and windows, gallons needed, and estimated cost.
How to Use This Paint Calculator
- Choose your Room Shape — Rectangle or L-Shape.
- Select your Unit System — Feet or Meters.
- Enter the room Dimensions (length, width, height).
- Enter the number of Doors and Windows to subtract from the wall area.
- Choose 1 or 2 coats of paint and adjust coverage per gallon if needed.
- Optionally enter the price per gallon to get a cost estimate.
- Click Calculate to see paintable area, gallons needed, and estimated cost.
Formula
Door Area = 21 sq ft per standard door (3’ × 7’)
Window Area = 15 sq ft per standard window (3’ × 5’)
Paintable Area = Wall Area − (Door Area × Doors) − (Window Area × Windows)
Gallons = (Paintable Area × Coats) / Coverage per Gallon
Standard door and window sizes are used by default. All dimensions are converted to feet if using meters. Coverage defaults to 350 sq ft per gallon, which is typical for latex paint on smooth walls.
Examples
12 ft × 10 ft × 8 ft, 1 door, 1 window, 2 coats:
Wall Area = 2×(12+10)×8 = 352 sq ft
Net = 352 − 21 − 15 = 316 sq ft
Gallons = (316 × 2) / 350 = 1.81 → 2 gallons
20 ft × 15 ft × 9 ft, 2 doors, 3 windows, 2 coats:
Wall Area = 2×(20+15)×9 = 630 sq ft
Net = 630 − 42 − 45 = 543 sq ft
Gallons = (543 × 2) / 350 = 3.10 → 4 gallons
8 ft × 6 ft × 8 ft, 1 door, 1 window, 1 coat:
Wall Area = 2×(8+6)×8 = 224 sq ft
Net = 224 − 21 − 15 = 188 sq ft
Gallons = (188 × 1) / 350 = 0.54 → 1 gallon
Frequently Asked Questions
How much paint do I need for a room?
For a standard 12×10 ft room with 8 ft ceilings, you need approximately 1.8–2 gallons for 2 coats. Use this calculator with your exact room dimensions for a precise estimate.
How many square feet does a gallon of paint cover?
A gallon of paint typically covers 350–400 sq ft for one coat on a smooth surface. Textured or porous surfaces may reduce coverage to 250–300 sq ft per gallon. Check the paint can label for exact coverage.
Should I use 1 or 2 coats of paint?
Two coats are recommended for most projects for better coverage, color accuracy, and durability. One coat may suffice for painting over a similar color or using paint-and-primer combos. Dark or bold colors usually require two coats minimum.
How much extra paint should I buy?
Buy about 10–20% more than your calculated amount. This accounts for uneven coverage, touch-ups, and waste. Having extra paint also ensures color matching for future touch-ups.