How much paint do I need?
Measure the walls, take away doors and windows, multiply by the coats and divide by what a gallon covers. Here is the rule, worked examples for one wall and a whole room, and a free calculator that does it for you.
How much paint do I need for one wall?
Multiply the wall's width by its height, subtract each window and door, then multiply by the number of coats. Divide by the coverage: about 375 ft² per gallon for typical US interior paint, or about 10 m² per litre for UK and European emulsion. Round up to the next whole can.
litres = (wall area − openings) × coats ÷ 10 m²
Worked example: one wall
- Wall 14 ft wide × 9 ft high = 126 ft² (4.2 m × 2.7 m = 11.34 m²).
- Take away a door, 3 ft × 7 ft = 21 ft² (0.9 m × 2.1 m = 1.89 m²). That leaves 105 ft² (9.45 m²).
- Two coats: 210 ft² (18.9 m²).
- 210 ÷ 375 = 0.56, so buy 1 gallon. In litres, 18.9 ÷ 10 = 1.89, so buy 2 litres.
How much paint do I need for a whole room?
Add the four walls together: the distance around the room times the ceiling height. Take off every door and window, multiply by the coats and divide by the coverage. The ceiling is a separate product, usually a flat ceiling white, so work it out on its own from the floor area.
- Room 12 × 14 ft with an 8 ft ceiling: 2 × (12 + 14) = 52 ft around, × 8 ft = 416 ft² of wall.
- Take away one door (21 ft²) and one window (15 ft²): 380 ft².
- Two coats: 760 ft². 760 ÷ 375 = 2.03, so 2 gallons is just short: buy 2 gallons and a quart, or 3 gallons.
- Ceiling: 12 × 14 = 168 ft², two coats = 336 ft², 336 ÷ 375 = 0.9, so 1 gallon of ceiling paint.
How much does a gallon of paint cover?
Most US interior paints state 350 to 400 ft² per gallon on a smooth, primed wall, so Roomveil uses about 375 ft². UK and European emulsion is sold in litres and covers about 10 m² per litre. Rough, porous or textured walls drink more paint, so read the label on the product you are buying and round up.
How many coats of paint do I need?
Two coats is normal for a repaint, because the second coat evens out patchy areas and gives the color its true depth. Use three coats when a light color goes over a dark one. A single coat only works when the new color is very close to the old one.
Do I need a primer?
Use a primer on new drywall or bare plaster, on patched areas, and for a big color change such as light over dark or dark over light. Primer is its own product with its own coverage on the can, so count it as one extra coat of primer rather than of your finish paint.
See the color before you buy
Roomveil lets you tap a color and see it on a photo of your own wall, with the shadows and light from your room kept. It works out the gallons or litres for one wall or for a whole room, with doors and windows taken off and the ceiling added if you want it, in any unit you measured in.
These are common rules of thumb and code minimums, given for planning. Always check the product label, the maker's instructions and your local building code before you buy or build.