How to use this paint calculator
- Measure the length and width of the room and the wall height.
- Count doors and windows (they are subtracted automatically).
- Choose the number of coats: 2 is standard, 1 may be enough for a similar color.
- Round up to the nearest can size.
Example
A 12 × 12 ft room with 8 ft walls, one door and two windows has about 333 sq ft of wall to paint. Two coats means 666 sq ft (61.9 m²), which needs 1.9 gallons of paint. In practice you would buy 2 gallons.
What to know before you buy
Choosing a finish
Flat and matte finishes hide wall imperfections and suit ceilings and living rooms. Eggshell and satin are washable and work well in hallways and bedrooms. Semi-gloss is best for trim, doors, kitchens and bathrooms because it resists moisture and cleans easily.
How much for trim and ceilings
Trim and doors usually need about a quart per room for two coats. Ceilings are often painted with flat ceiling paint; include them with the option above or calculate them separately using the room's floor area.
Paint for walls with 2 coats (1 door, 2 windows, 8 ft ceilings)
| Room size | Paint needed | Liters |
|---|---|---|
| 10 × 10 ft | 1.5 gallons | 5.8 L |
| 10 × 12 ft | 1.7 gallons | 6.5 L |
| 12 × 12 ft | 1.9 gallons | 7.2 L |
| 12 × 15 ft | 2.2 gallons | 8.2 L |
| 14 × 16 ft | 2.5 gallons | 9.3 L |
| 15 × 20 ft | 2.9 gallons | 11 L |
Formula
Wall area = 2 × (length + width) × height − doors (≈ 21 sq ft each) − windows (≈ 15 sq ft each). Paint = area × coats ÷ 350 sq ft per gallon (≈ 8.6 m² per liter).
Tips from the pros
- A gallon covers about 350–400 sq ft per coat on smooth, primed walls; textured walls may need 20% more.
- Buy one container large enough for the whole job, or mix (box) several gallons together for a consistent color.
- Use primer on new drywall, patched areas and when covering a dark color with a light one.
Common mistakes to avoid
- Buying for one coat: most colors need two coats for even coverage.
- Painting over glossy surfaces without sanding or priming, which leads to peeling.
Frequently asked questions
How much does a gallon of paint cover?
About 350–400 square feet per coat on smooth walls; less on rough or porous surfaces.
Do I need primer?
Use primer on new drywall, bare wood, stains or when making a dramatic color change.
How much paint for a 12x12 room?
About 1.9 gallons for two coats on the walls with 8 ft ceilings, one door and two windows, so buy 2 gallons.
How much paint does a ceiling need?
Use the floor area: a 12 × 12 ft ceiling is 144 sq ft, which needs a bit less than half a gallon per coat.