Find out how much paint you need for walls, a whole room or a ceiling, from the size, the number of coats and the coverage of your paint.
Paint Coverage Guidelines
Standard Coverage Rates:
- Smooth walls: 400-450 sq ft per gallon
- Average walls: 350-400 sq ft per gallon
- Textured/rough walls: 250-350 sq ft per gallon
- Porous surfaces: 200-300 sq ft per gallon
Tips for Accurate Estimation:
- Measure all walls and multiply length by height
- Standard door size: 20 sq ft, standard window: 15 sq ft
- Always buy extra paint (10% waste factor recommended)
- Dark colors may require an additional coat
- Primer may be needed for new drywall or color changes
What this paint calculator does
- Walls: wall length and height, coats and coverage to gallons and quarts.
- Room: room length, width and height, taking off doors and windows.
- Ceiling: ceiling length and width.
- Advanced: a total area with a waste factor, rounded up to the next half gallon, with the cost at your price per gallon.
How it is calculated
Paint needed = area × number of coats ÷ coverage per gallon. Coverage defaults to 350 square feet per gallon, a common planning figure; check the coverage stated on your paint can, as it varies by product, and some manufacturers quote about 400. Recommended amounts are rounded up to the next half gallon.
In the Room tab the wall area is the room’s perimeter × height, minus 20 square feet for each door and 15 square feet for each window.
Worked examples: 40 ft of wall, 8 ft high, with 2 coats is 640 sq ft of coverage, or 1.83 gallons, so buy 2 gallons. A 12 ft × 10 ft room with 8 ft walls, 1 door, 2 windows and 2 coats has 302 sq ft to paint, or 1.73 gallons. A 12 × 10 ft ceiling with 2 coats needs 0.69 gallons. In the Advanced tab, 500 sq ft with 2 coats and 10% waste is 3.14 gallons, so 3.5 gallons, or $140 at $40 a gallon.
Things to keep in mind
The door and window sizes are typical figures, so enter fewer or more openings to match your room. Primer, rough or porous surfaces, and big colour changes can all increase the paint you need. If the doors and windows take up more than the wall area, the calculator will ask you to check your numbers. These are planning estimates only. Measure your own project carefully, check product labels and local building codes, and confirm quantities with your supplier or a qualified contractor before you buy.
Frequently asked questions
How many coats should I allow for?
Two coats is common. A dramatic colour change or a bare surface may need more.
Should I paint the ceiling and walls with the same amount?
Calculate them separately, because the area and sometimes the product are different.
Looking for more? See all our free construction and home improvement calculators.