How Much Paint for a 12×12 Room?
A 12×12 room with an 8 ft ceiling has 384 sq ft of gross wall area. Subtract 1 door (20 sq ft) and 2 windows (30 sq ft) and the paintable area is 334 sq ft. At 350 sq ft/gal: 1 gallon per coat, 2 gallons for two coats.
The worked math for a 12×12×8 room
The four walls of a 12×12 room with 8 ft ceilings total:
- Gross wall area: 2 × (12 + 12) × 8 = 384 sq ft
- Subtract 1 door: −20 sq ft
- Subtract 2 windows: −30 sq ft
- Paintable area: 384 − 50 = 334 sq ft
- At 350 sq ft/gal, 1 coat: 334 ÷ 350 = 0.95 gal → buy 1 gallon
- At 350 sq ft/gal, 2 coats: 334 × 2 ÷ 350 = 1.91 gal → buy 2 gallons
Adjust the inputs below for your actual door/window count, ceiling height, or coverage rate.
Room Dimensions
Openings & Coats
How the math works
Step 1 — gross wall area
gross_wall = 2 × (length + width) × ceiling_height Step 2 — subtract openings
paintable = gross_wall − (doors × 20) − (windows × 15) Each standard 36×80 in door = 20.0 sq ft. Average window = 15 sq ft (industry convention). Paintable area is clamped to ≥0.
Step 3 — gallons
gallons_to_buy = ⌈ (paintable × coats) ÷ coverage ⌉ Coverage defaults to 350 sq ft/gal — the conservative figure used by Sherwin-Williams, Benjamin Moore and Behr field guides. Always round up to whole gallons; running out mid-job risks a dye-lot mismatch.
What if my 12×12 room has different details?
The calculator above is pre-set to 12×12 ft and 8 ft ceilings — the most common US bedroom and living room configuration. If your room differs:
- More doors (e.g. closet + entry): add them to the count. Each door deducts 20 sq ft.
- Taller ceiling (9 or 10 ft): change the ceiling height field — the gross wall area increases proportionally.
- Textured walls: switch the coverage to 250 or 300 sq ft/gal instead of 350.
- Dark color change: choose 3 coats instead of 2.
Frequently Asked Questions
At 350 sq ft/gal, a 12×12×8 room with 1 door and 2 windows has 334 sq ft paintable area. One coat: 334 ÷ 350 = 0.95 gallons → buy 1 gallon. Two coats: 334 × 2 ÷ 350 = 1.91 gallons → buy 2 gallons. Two coats is strongly recommended for even, durable coverage.
If the walls are new drywall, have been patched, or you are making a dramatic color change (dark to light), yes — primer is needed first. At 250 sq ft/gal, 334 sq ft of paintable area needs 1.34 gallons of primer → buy 2 gallons. Use the primer calculator on this site for an exact count.
A 12×12 ceiling is 144 sq ft. At 350 sq ft/gal, 1 coat needs 0.41 gallons and 2 coats needs 0.82 gallons — either way, 1 gallon covers 2 coats. Ceiling paint is a separate product; use the ceiling paint calculator on this site.
No — not for walls. Two coats of a 12×12×8 room (with 1 door and 2 windows) need 1.91 gallons, so you buy 2 gallons. The common belief that "one gallon covers a 12×12 room" refers to one coat only, which is what Benjamin Moore's approximate claim of "400 sq ft/gal" targets (1 coat on a 12×12 with zero openings = 384 sq ft, just under 400).