Paint Coverage Formulas
Basic Coverage Formula
Gallons = (Total Area × Number of Coats) ÷ Coverage Rate
Where:
- Total Area is measured in square feet
- Coverage Rate is typically 350-400 square feet per gallon
- Number of Coats is usually 2 for interior walls
Wall Area Calculation
Wall Area = (Length + Width) × 2 × Height
This formula calculates the total surface area of all four walls in a rectangular room.
Adjustments for Doors and Windows
Adjusted Area = Wall Area - (Doors × 20) - (Windows × 15)
Standard sizes:
- Standard door: 20 square feet
- Standard window: 15 square feet
- Large window: 35 square feet
Complete Example
Scenario: 12×12 room with 8-foot ceilings
Step 1: Calculate wall area
(12 + 12) × 2 × 8 = 384 sq ft
Step 2: Subtract door and window
384 - 20 - 15 = 349 sq ft
Step 3: Calculate gallons for 2 coats
(349 × 2) ÷ 375 = 1.86 gallons
Result: Purchase 2 gallons of paint