The Basic Formula
Paint needed = (Total wall area ÷ Coverage per gallon) × Number of coats
Step 1: Calculate Wall Area
Wall area = Perimeter × Height - Doors & Windows
- Standard door: 21 sq ft
- Standard window: 15 sq ft
Step 2: Check Paint Coverage
- Budget paint: 300-350 sqft/gallon
- Mid-range: 350-400 sqft/gallon
- Premium: 400-450 sqft/gallon
Step 3: Account for Coats
Most jobs need 2 coats. Add 3rd coat if changing from dark to light.
Quick Reference by Flat Type
- 3-room HDB: 2-3 gallons
- 4-room HDB: 3-4 gallons
- 5-room HDB: 4-5 gallons
Pro Tip
Always buy 10% extra for touch-ups and future repairs.