Estimate how many gallons of paint you need for walls and ceilings. Enter your room dimensions, subtract doors and windows, and choose the number of coats.
Round up to the nearest quart or gallon when purchasing.
Enter the room length, width, and wall height in feet
Enter the number of standard doors and windows to subtract their area
Choose the number of coats (2 is standard for most projects) and paint coverage
Optionally check "Include ceiling" to add the ceiling area to your total
The perimeter of the room is multiplied by the wall height to get total wall area. Standard door area (~21 sq ft) and window area (~15 sq ft) are subtracted. The net area is divided by paint coverage and multiplied by the number of coats.
Average bedroom: 12 × 10 ft, 8 ft walls, 1 door, 2 windows, 2 coats
Perimeter 44 ft × 8 ft = 352 sq ft. Subtract 21 + 30 = 51 sq ft → 301 net sq ft × 2 coats = 602 sq ft ÷ 350 = 1.72 gal
Result: ~2 gallons (buy one 2-qt kit or 2 gallons)
Living room: 20 × 15 ft, 9 ft walls, 2 doors, 4 windows, 2 coats
Perimeter 70 ft × 9 ft = 630 sq ft. Subtract 42 + 60 = 102 → 528 sq ft × 2 ÷ 350 = 3.02 gal
Result: ~3.1 gallons (buy 4 gallons to be safe)
Small bathroom: 8 × 6 ft, 8 ft walls, 1 door, 1 window, 2 coats
Perimeter 28 ft × 8 ft = 224 sq ft. Subtract 21 + 15 = 36 → 188 sq ft × 2 ÷ 350 = 1.07 gal
Result: ~1.1 gallons (buy 1 gallon + 1 quart)
Always buy paint from the same batch (same lot number) to avoid slight color variations. Mix multiple cans together in a large bucket before painting - a technique called "boxing" the paint.