BuildCalc Guides · Paint
How Much Paint for a 12×12 Room?
One of the most common DIY paint questions, with a deceptively simple answer. Here is the math, the openings to subtract, and what changes the number for your specific room.
The math
Paint quantity is wall area times coats divided by the coverage per gallon. For a 12 by 12 foot room with 8 foot ceilings, one standard door, and two standard windows:
- Perimeter = 2 × (length + width) = 2 × (12 + 12) = 48 ft.
- Wall area = perimeter × ceiling height = 48 × 8 = 384 ft².
- Subtract openings. A standard door is about 21 ft² (3' × 7') and a standard window is about 15 ft² (3' × 5'). For 1 door + 2 windows that is 21 + 30 = 51 ft² off.
- Net paintable wall = 384 − 51 = 333 ft².
- Multiply by coats. At 2 coats, you are painting 666 ft² total.
- Divide by coverage. At 350 ft²/gallon, 666 / 350 = 1.9 → round up to 2 gallons.
By room size (8 ft ceilings, 2 coats)
Same assumptions: 1 door, 2 windows, 350 ft²/gallon coverage. Wall area is shown net of openings.
| Room (L×W × H) | Net wall | 2 coats | Buy |
|---|---|---|---|
| 10×10 × 8 | 269 ft² | 538 ft² | 2 gal |
| 12×12 × 8 | 333 ft² | 666 ft² | 2 gal |
| 12×12 × 9 | 381 ft² | 762 ft² | 3 gal |
| 14×14 × 8 | 397 ft² | 794 ft² | 3 gal |
| 16×16 × 8 | 461 ft² | 922 ft² | 3 gal |
Rounded up to whole gallons. Add about 0.5 gallon if also doing the ceiling at 2 coats.
What changes the number
- Coverage rating. 350 ft²/gal is average. Premium one-coat paints quote 400; flat ceiling paint also covers a touch more. Primer covers less — plan 250 to 300 ft²/gal.
- Surface texture. Smooth drywall hits the quoted coverage. Knockdown, orange peel or popcorn textures eat 15 to 25 percent more paint per coat.
- Color change. A big color jump (dark over light, or covering a saturated color) usually needs a primer plus two finish coats. Same-color repaints can sometimes get by with one.
- Trim and doors. These are typically a different finish (semi-gloss) from the wall paint and bought separately. Plan about 1 quart per room for trim.
- Texture and porosity. New drywall and bare patches drink paint until they are sealed. Spot-prime patches before the first finish coat.
Calculate for your own room
BuildCalc's paint calculator takes the room dimensions, your number of doors and windows, coats and coverage rating, and returns the exact gallon count. Add a price per gallon for a live cost estimate.
Open the paint calculator →FAQ
How many gallons of paint do I need for a 12x12 room?+
Plan on about 2 gallons for a standard 12 by 12 foot room with 8 ft ceilings, one door and two windows, painted in 2 coats with average 350 sq ft/gallon coverage. That is about 1.9 gallons exactly, rounded up to whole cans.
Does one gallon of paint really cover 350 sq ft?+
Most interior latex paints quote 350 to 400 sq ft per gallon on smooth, primed drywall. Textured walls and bigger color changes drop that closer to 300, and a primer coat covers less still (250 to 350). Always pour back into the can to read the manufacturer-stated coverage.
How many coats of paint do I need?+
Two coats is the default for an even, finished look. Touch-ups and same-color repaints can sometimes get away with one. A dramatic color change — a dark color over white, or vice versa — typically needs a primer plus two coats.
Should I subtract doors and windows from the paintable area?+
Yes. Subtracting roughly 21 sq ft per standard door and 15 sq ft per window keeps you from over-ordering on a small room. The savings get bigger as the room shrinks — for a 12x12 the openings cut about 13 percent off the wall area.
Do I paint the ceiling the same color or separately?+
Most people paint ceilings white in a flat or matte finish, separate from the wall color. That keeps the room feeling taller and lets the wall paint take a small amount of overspray near the corners. If you plan to do the ceiling too, add about 144 sq ft (12 by 12) of paintable area — roughly half a gallon at 2 coats.
How much extra paint should I buy for touch-ups?+
A spare quart per color is usually enough for touch-ups over a year or two. Paint stores can match a sample, but a quart of the original batch matches perfectly. Label it with the room and date when you store it.
Related guides
- How many bags of concrete for a 10×10 slab? — outdoor projects often start with a slab.
- How to calculate stair stringers — for the basement or addition you are painting next.
- How many cubic yards of mulch for 1,000 sq ft? — exterior projects start with the beds along the foundation.