Paint Calculator
Calculate exactly how much paint you need for any room. Accounts for doors, windows, and number of coats.
How to Use the Paint Calculator
- Enter the room length, width, and wall height in feet.
- Enter the number of doors and windows — their area is deducted automatically (21 sq ft per door, 15 per window).
- Choose the number of coats (2 is recommended for most walls).
- Tick paint the ceiling if needed.
- Click Calculate to see paintable area, gallons, and liters required.
Formula & Method
Wall Area = 2 x (Length + Width) x Height
Net Area = Wall Area + Ceiling - (Doors x 21 + Windows x 15)
Gallons = (Net Area x Coats) / 350
One gallon of paint typically covers about 350 square feet per coat (one liter covers about 8.6 square meters). Textured walls, dark-to-light color changes, and unprimed surfaces may need 10-20% more.
Examples
| Room Size | Wall Area (net) | Coats | Paint Needed |
|---|---|---|---|
| 10 x 12 ft, 9 ft walls | 345 sq ft | 2 | 1.97 gal (7.5 L) |
| 15 x 12 ft, 9 ft walls | 435 sq ft | 2 | 2.49 gal (9.4 L) |
| 20 x 15 ft, 10 ft walls | 649 sq ft | 2 | 3.71 gal (14 L) |
| 12 x 12 ft + ceiling | 525 sq ft | 2 | 3.0 gal (11.4 L) |
Frequently Asked Questions
How much paint do I need for a 12x12 room?
A 12 x 12 ft room with 9 ft walls, one door, and one window needs about 2.3 gallons (8.8 liters) for two coats on the walls. Add the ceiling and you need about 3 gallons.
How much area does one gallon of paint cover?
One gallon covers approximately 350 square feet per coat on smooth, primed walls. Rough or textured surfaces may only get 250-300 sq ft per gallon.
Should I buy extra paint?
Yes — buy 10% extra for touch-ups and future repairs. Rounding up to the next full gallon is standard practice. Leftover paint keeps for years if sealed properly.
Do I always need two coats?
Two coats give the best color depth and durability. One coat may suffice when repainting a similar color over primed walls. Dramatic color changes (dark to light) may need primer plus two coats.
How do I measure an odd-shaped room?
Break the room into rectangular sections, calculate each wall separately, then add them together. For sloped ceilings, measure the wall at its average height.
People Also Ask
How much paint for 1000 square feet?
For 1000 sq ft of paintable area with two coats, you need about 5.7 gallons (21.6 liters), based on 350 sq ft coverage per gallon per coat.
How many liters of paint per square meter?
One liter covers about 8-9 square meters per coat. For two coats over 50 square meters, you need roughly 12 liters.
Does primer count as a coat?
No. Primer is separate and goes on first over bare drywall, stains, or drastic color changes. Plan for primer coverage the same way — about 350 sq ft per gallon.