Gallons for your room — walls, ceiling if you want it, minus doors and windows, times the number of coats.
Feet
Feet
Feet — 8 or 9 are typical
Each door ≈ 21 sq ft
Each window ≈ 15 sq ft
Item
Amount
Wall paint
Ceiling paint
Primer
Paintable area
Estimated paint cost
One gallon covers ~350 sq ft per coat on smooth, primed walls (less on rough or unprimed surfaces). Two coats over a darker color is the norm — a tinted primer can save a third coat.
🛒 Shopping list
Item
Qty
Wall paint
Ceiling paint (flat white)
Primer
Painter's tape, 1.5″
Roller covers (3/8″ nap), brushes, tray, drop cloths
1 kit
✅ Project checklist
Wash walls (TSP substitute for kitchens/baths); let dry fully
Patch nail holes and cracks; sand smooth; spot-prime patches
Tape trim and fixtures; drop cloths down before the can opens
Cut in edges first, then roll in W-pattern sections while the edge is wet
Second coat after the recoat window on the can (usually 2–4 hours)
Pull tape while the final coat is still slightly tacky for a clean line
How the math works
Wall area = room perimeter × ceiling height, minus ~21 sq ft per door and ~15 sq ft per window. Gallons = area × coats ÷ 350 sq ft of coverage, rounded up — paint is sold in whole gallons and quarts (0.9 gal of need still buys a gallon, or a gallon minus one quart if you're brave). Ceiling paint is figured separately at one coat.
For estimation only. Actual coverage varies by paint, surface and color depth — check the can's stated coverage.