Paint Coverage Calculator: Gallons of Paint & Primer for Any Room
Enter room dimensions or total wall area, doors, windows, coats and surface texture to get exact gallons — rounded to the buckets and cans you'll actually buy.
1Measure the walls
−21 sq. ft each
−15 sq. ft each
2Surface & paint
Previously painted, smooth walls in good condition. Prime only for big color changes or stains.
Your paint estimate
Paint to buy
2 × 1-gal cans
Net paintable area
333 sq. ft
Primer
Not included
Trim paint
Not included
Coverage: 350 sq. ft/gal per coat (conservative end of 350–400). Buckets are suggested when cans would cost as much.
- DIY — paint, primer & supplies$129
$84 paint + $0 primer + $45 supplies
- Pro painter (interior)$666 – $1,499
$2.00–$4.50 per sq. ft incl. labor & materials
Painting it yourself saves about $537–$1,370.
Paint shopping list
| Wall paint (2 coats)1.9 gal needed · Smooth drywall (painted) | 2 × 1-gal cans |
| Roller covers + frame, angled brush, tray3/8" nap smooth · 1/2" textured | 1 kit |
| Painter's tape & drop cloths | 1 set |
Have all cans of the same color 'boxed' (mixed together) for a consistent finish.
How much paint for a room? Quick-reference table
Two coats on smooth, previously painted drywall at 350 sq. ft per gallon, walls only, mid-grade (most popular) paint at $42/gallon.
| Room | Net wall area | Gallons (2 coats) | Buy | DIY cost | Pro painter |
|---|---|---|---|---|---|
| Small bathroom8×5 ft, 8 ft ceiling · 1 door, 0 windows | 187 sq. ft | 1.07 | 1 × 1-gal can + 1 × quart | $102 | $374–$842 |
| Bedroom12×12 ft, 8 ft ceiling · 1 door, 2 windows | 333 sq. ft | 1.9 | 2 × 1-gal cans | $129 | $666–$1,499 |
| Primary bedroom14×16 ft, 9 ft ceiling · 2 doors, 3 windows | 453 sq. ft | 2.59 | 3 × 1-gal cans | $171 | $906–$2,039 |
| Living room16×20 ft, 9 ft ceiling · 2 doors, 4 windows | 546 sq. ft | 3.12 | 3 × 1-gal cans + 1 × quart | $186 | $1,092–$2,457 |
| Open great room20×24 ft, 10 ft ceiling · 2 doors, 6 windows | 748 sq. ft | 4.27 | 1 × 5-gal bucket | $234 | $1,496–$3,366 |
Paint coverage by surface
| Surface | Paint (sq. ft/gal) | Primer (sq. ft/gal) | Prime? |
|---|---|---|---|
| Smooth drywall (painted) (interior) | 350–400 | 300 | If needed |
| New (unpainted) drywall (interior) | 300–350 | 250 | Yes |
| Textured drywall (knockdown / orange peel) (interior) | 250–300 | 225 | If needed |
| Textured / stucco / masonry (exterior) | 200–250 | 150 | Yes |
| Wood or fiber-cement siding (exterior) | 250–350 | 250 | If needed |
| Vinyl or aluminum siding (exterior) | 350–400 | 300 | If needed |
The paint formula, step by step
Gallons = ((2 × (L + W) × H) − 21 × doors − 15 × windows) × coats ÷ coverage
- Measure the walls. Add up the room perimeter (2 × length + 2 × width) and multiply by the ceiling height.
- Subtract openings. Subtract about 21 sq. ft per door and 15 sq. ft per window.
- Multiply by coats. Multiply the net area by the number of coats — usually 2.
- Divide by coverage. Divide by the spread rate: 350–400 sq. ft/gal on smooth drywall, 200–250 on stucco or masonry.
- Round to containers. Round up to 1-gallon cans, and switch to a 5-gallon bucket once you need about 4.5 gallons or more.
Example: a 12 × 12 ft bedroom with 8 ft ceilings has 384 sq. ft of wall. Minus one door and two windows (51 sq. ft) leaves 333 sq. ft. Two coats ÷ 350 sq. ft/gal = 1.9 gallons → buy 2 × 1-gal cans.
Painting tips that save paint (and money)
- Tint your primer toward the finish color — it can save a full coat when covering dark colors.
- Buy everything for one color at once and mix ("box") the cans together for consistent sheen and color.
- A 5-gallon bucket with a roller screen is faster and cheaper than a tray for rooms over ~400 sq. ft.
- Ceilings: flat ceiling white covers about 350–400 sq. ft/gal; add 10% for heavily textured popcorn.
Frequently Asked Questions
How many square feet does a gallon of paint cover?
Most interior paints cover 350–400 sq. ft per gallon per coat on smooth, previously painted drywall. Textured walls, stucco and masonry drop that to 200–250 sq. ft per gallon, so this calculator uses the conservative end of each range.
How much paint do I need for a 12×12 room?
A 12×12 room with 8 ft ceilings has 384 sq. ft of wall. After subtracting one door (21 sq. ft) and two windows (30 sq. ft), that's 333 sq. ft. Two coats at 350 sq. ft/gal need 1.9 gallons — buy 2 one-gallon cans.
When should I buy a 5-gallon bucket instead of gallon cans?
A 5-gallon bucket usually costs about the same as 4–4.5 single gallons, so once you need 4.5 gallons or more of the same color, the bucket is the better deal. It also keeps the color consistent across walls.
Do I need primer before painting?
Prime new drywall, bare wood, patched areas, stains and porous masonry, or when you're making a dramatic color change (dark to light). Previously painted walls in good condition usually don't need a separate primer.