Wall Area Formula
For a rectangular room, use the room length, room width and wall height:
Wall Area = 2 x (Length + Width) x Wall Height
This formula estimates the total area of the four walls before subtracting openings such as doors and windows.
Subtract Doors and Windows
Doors and windows are usually not painted, so their areas can be deducted from the wall area.
Opening Area = Opening Width x Opening Height
If there are multiple doors or windows of the same size, multiply the opening area by the number of openings.
Handle Unusual Room Shapes
For rooms that are not rectangular, divide the walls into smaller measurable sections. Calculate each section separately, then add the areas together before subtracting openings.
Turn Wall Area Into a Paint Estimate
Once you have the paintable wall area, combine it with coverage and number of coats. You can do this manually or use the Interior Tailor paint calculator to estimate paint quantity from your measurements.