Paint Calculator
Gallons of paint for a room, walls and ceilingRuns in your browser
Rough material cost
$80Default prices are rough 2026 US big-box averages before tax and delivery. Edit them to match quotes from your local supplier.
Material estimates only. Round up, buy a little extra, and check with your supplier. Structural work (footings, framing, roofs) must follow local building codes; consult a licensed contractor where required.
How it works
Formulas
Wall area = 2 × (length + width) × height − 21 sq ft per door − 15 sq ft per windowGallons = area × coats ÷ coverage per gallonWorked example
Input: 12 × 12 ft room, 8 ft walls, 1 door, 2 windows, 2 coats, 350 sq ft/gal.
- Walls: 2 × 24 × 8 = 384 sq ft − 21 − 30 = 333 sq ft.
- 333 × 2 ÷ 350 = 1.90 gallons.
Result: Buy 2 gallons.
Limits
- Trim, doors and cabinets are not included.
- Three quarts are rounded up to a gallon because a gallon usually costs about the same.
How to use
- 1Enter the room length, width and wall height.
- 2Enter the number of doors and windows to subtract.
- 3Set coats (2 is typical) and the coverage printed on the can.
- 4Buy the gallons and quarts shown.
FAQ
How much does a gallon of paint cover?
Most interior paints cover 350–400 square feet per gallon per coat on smooth, primed walls. Rough or porous surfaces and big color changes need more.
Do I need two coats?
Usually yes for even color, especially over a different color. Paint-and-primer products may cover in one coat over a similar color.
How much paint for a 12 × 12 room?
With 8 ft walls, one door, two windows and two coats: about 333 sq ft of wall × 2 coats ÷ 350 = 1.9 gallons, so 2 gallons.
Can I use metric units?
Yes. Switch to Metric and enter meters and centimeters; results show cubic meters, square meters or tonnes alongside US units.