The Paint Calculator estimates how many gallons of paint you need for your project based on room dimensions, number of coats, and surface type. It accounts for doors, windows, and trim to give you an accurate purchase quantity and avoid costly over-buying or mid-project shortages.
How the Formula Works
Paint needed (gallons) = (Total wall area − Windows − Doors) × Number of coats ÷ Coverage rate. Standard coverage: 350–400 sq ft per gallon.
How to Use This Calculator
Enter room dimensions (length, width, height)
Enter the number of doors and windows to subtract
Select the number of coats (1 or 2)
View gallons needed and estimated cost
Tips & Best Practices
Always buy slightly more than calculated — running out mid-wall creates visible color differences
Two thin coats provide better coverage than one thick coat
Dark colors over light typically need 2 coats; light over dark may need 3
One gallon covers about 350–400 sq ft on smooth surfaces
Keep leftover paint for touch-ups — label it with the room and date
Important Limitations
Coverage varies by paint brand, type (flat vs. semi-gloss), and application method (roller vs. brush vs. sprayer)
Does not account for ceiling painting — calculate that separately
Textured surfaces can require 25–40% more paint than smooth walls