Paint guide
Plan your paint project
How to measure a room for paint
Measure the length and width of the floor and the height of the walls in feet. The wall area is the perimeter times the height: 2 × (length + width) × height. You do not need to measure each wall on its own unless the room is not a rectangle.
Count the doors and windows. Each one is a patch of wall you will not paint, so the calculators subtract a standard size for each. Closets with their own walls are easier to measure as a separate small room.
One coat or two?
Plan on two coats for almost every repaint. One coat can work when the new color is close to the old one and the wall is clean and already painted in the same sheen. A big change in color, especially dark to light, usually needs a coat of primer first and then two finish coats.
New drywall and patched areas soak up the first coat. Prime them, or use the bare surface coverage figure for the first coat.
Buying gallons and quarts
- Round the total up, then split it into gallons and quarts. Three or more quarts of remainder usually cost more than one extra gallon.
- Buy all the paint for one room at the same time so it comes from the same tinting. If cans are mixed on different days, pour them together in a bucket before you start.
- Keep a little extra. A labeled half quart makes future touch-ups match.
Paint numbers worth knowing
| Item | Typical figure | Why it matters |
|---|---|---|
| Coverage, smooth primed wall | 350–400 sq ft per gallon | Printed on most interior wall paint labels |
| Coverage, textured wall | About 300 sq ft per gallon | Texture adds surface area |
| Coverage, bare drywall or porous surface | About 250 sq ft per gallon | The first coat soaks in |
| Standard door | About 20 sq ft | Subtracted from the wall area |
| Standard window | About 15 sq ft | Subtracted from the wall area |
| One quart | 1/4 gallon | Cheaper than a full gallon for a small remainder |
Common mistakes
- Using floor area instead of wall area.
- Forgetting the second coat.
- Using the label coverage for a textured or unprimed wall.
- Buying a fresh can of a custom color weeks later and getting a slightly different shade.
Frequently asked questions
How many square feet does a gallon of paint cover?
Most interior wall paints list 350 to 400 sq ft per gallon for one coat on a smooth, primed wall. Textured and unprimed walls cover less, often 250 to 300 sq ft per gallon.
How much paint do I need for a 12 × 12 room?
With 8 ft walls, one door and two windows, a 12 × 12 ft room has about 334 sq ft of paintable wall. Two coats at 350 sq ft per gallon, plus 10% for touch-ups, comes to about 2.1 gallons: buy 2 gallons and 1 quart.
Do I need different paint for the ceiling?
Most people use a flat ceiling paint because it hides small flaws and reflects light evenly. Use the ceiling paint calculator for the amount, since a ceiling is measured from the floor area, not the walls.
Should I subtract doors and windows?
Yes. Doors and windows are usually 15 to 20 sq ft each. In a small room they can add up to more than half a gallon over two coats.
Sources
- Sherwin-Williams, How to Use Paint Calculator
- Benjamin Moore, Paint Calculator