Paint Calculator: How Much Paint Do I Need?
Enter the room size and the number of doors and windows. You'll get how many gallons and quarts to buy for the walls, and optionally the ceiling, based on real coverage rates.
- Tested formulas
- Feet or metric
- Printable shopping list
2 What to buy
Updates as you type| Room perimeter | 48 ft |
|---|---|
| Gross wall area | 384 sq ft |
| Doors and windows deducted | 50 sq ft |
| Paintable wall area | 334 sq ft |
| Coverage used | 375 sq ft per gallon (9.2 m² per liter) |
Shopping list
Quick answer
A 12 × 12 ft room with 8 ft ceilings, one door and two windows has 334 sq ft of wall. Two coats at about 375 sq ft per gallon need 1.8 gallons, so buy 2 gallons. Add about a gallon for the ceiling.
Paint for common room sizes
| Room | Wall area | Walls | Ceiling |
|---|---|---|---|
| 10 × 10 ft | 270 sq ft | 1 gal + 2 qt | 1 gal |
| 10 × 12 ft | 302 sq ft | 2 gal | 1 gal |
| 12 × 12 ft | 334 sq ft | 2 gal | 1 gal |
| 12 × 14 ft | 366 sq ft | 2 gal | 1 gal |
| 14 × 16 ft | 430 sq ft | 2 gal + 2 qt | 1 gal + 2 qt |
| 16 × 20 ft | 526 sq ft | 3 gal | 2 gal |
8 ft walls, one door, two windows, two coats, smooth walls. Use the calculator above for your exact size.
How much paint does a room need?
A gallon of interior paint covers roughly 350–400 sq ft per coat on smooth, previously painted walls, and less on texture or bare drywall. The steps are:
- Perimeter × wall height = gross wall area
- Subtract about 20 sq ft per door and 15 sq ft per window
- Multiply by the number of coats, then divide by the coverage per gallon
Worked example: 12 × 12 ft bedroom, 8 ft ceilings
- Walls: 48 ft perimeter × 8 ft = 384 sq ft
- Minus 1 door and 2 windows (50 sq ft) = 334 sq ft
- 2 coats at 375 sq ft/gal = 1.78 gallons, so buy 2 gallons
Our calculator turns the total into cans you can actually buy. It uses quarts for small top-ups, but rounds three quarts up to a full gallon, because a gallon costs less than three quarts.
Do I need two coats?
Usually, yes. Two coats give even color and sheen, especially for big color changes, light colors over dark, or flat finishes. "Paint and primer in one" products can cover in one coat when repainting a similar color over a clean wall.
Coverage by surface
| Surface | Coverage per gallon |
|---|---|
| Smooth, previously painted | 350–400 sq ft |
| Light texture (orange peel, knockdown) | 300–350 sq ft |
| Heavy texture, popcorn, brick | 200–300 sq ft |
| New drywall (prime first) | Primer ~300 sq ft, then topcoats as above |
Buy all the paint for a room at once and box it: pour every can into a bucket and mix. Small tint differences between cans then can't show up as patches on the wall.
Frequently asked questions
How much paint do I need for a 12×12 room?
With 8 ft walls, one door and two windows, about 334 sq ft of wall. Two coats need about 1.8 gallons, so buy 2 gallons. Add about 1 gallon if you're painting the ceiling too.
How many square feet does a gallon of paint cover?
Most interior paints cover 350–400 sq ft per gallon per coat on smooth walls. Textured or porous surfaces drop to 250–300 sq ft.
Should I subtract windows and doors?
Yes, for accurate totals: about 20 sq ft per door and 15 sq ft per window. If you're also painting the trim, that's a separate, smaller amount of trim paint.
How much paint do I need for one wall?
Multiply the wall's width by its height and divide by the paint's coverage, about 375 sq ft per gallon on a smooth wall. A 12 × 8 ft wall is 96 sq ft, so two coats take about half a gallon; a quart is a quarter gallon.
Last reviewed 2026-10-21. See how we calculate for our sources and assumptions.