Paint Coverage Calculator
Estimate how many gallons of paint you need for your room. Accounts for doors, windows, and number of coats.
Unit System
Results
Total Wall Area
0 sq ft
Paintable Area
0 sq ft
Gallons Needed
0
Liters Needed
0
About This Calculator
This paint coverage calculator estimates how much interior wall paint you need for a rectangular room. It computes the total wall area using the perimeter and height, then subtracts standard-sized openings: each door is 21 sq ft (3 ft × 7 ft) and each window is 15 sq ft (3 ft × 5 ft). Coverage is based on the industry-standard rate of 350 sq ft per gallon. If you are painting with two coats (recommended for most projects), the calculator doubles the paintable area before dividing by coverage.
FAQ
Why does this calculator default to 2 coats?
Most paint manufacturers recommend two coats for even coverage and true color, especially when changing colors or painting over dark walls. A single coat may be sufficient for touch-ups or when using a paint-and-primer combo on a similar base color.
What if my doors or windows are non-standard sizes?
This calculator uses standard door (3 ft × 7 ft = 21 sq ft) and window (3 ft × 5 ft = 15 sq ft) sizes. If your openings are significantly larger (e.g., French doors, picture windows), you can set the count higher to subtract more area, or calculate the actual area manually and adjust.
Does 350 sq ft per gallon apply to all paints?
350 sq ft per gallon is the industry average for smooth, primed walls. Textured surfaces, bare drywall, or porous masonry may reduce coverage to 250–300 sq ft per gallon. Always check the coverage rate on your specific paint can.
How do I calculate paint for a ceiling?
For the ceiling, simply multiply the room length by the room width to get the ceiling area. Then divide by 350 sq ft (per gallon) and multiply by your number of coats. Add that to your wall paint estimate.