How much paint do I need?
Add every room you're painting and get the total gallons andproject cost in one estimate — rounded up only once, so you don't overbuy a half-gallon per room. Pick any of 15 brands to price it. Scroll down for the formula and a coverage chart if you'd rather calculate by hand.
PER-ROOM BREAKDOWN
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The paint formula
Every paint calculation is the same equation. Find your paintable area, multiply by how many coats you're doing, and divide by how far a gallon goes:
gallons = (paintable area in sq ft × coats) ÷ coverage per gallon
Coverage is the only number that changes by product. Premium interior wall paint covers about 350 to 400 sq ft per gallon; exterior, stucco, and stains cover less. The builder above does this for every room at once and rounds the combined total up only once, so you don't waste a partial can per room.
How to calculate the square footage of a room
- Measure the perimeter. Add all four wall lengths: 2 × length + 2 × width.
- Multiply by wall height. Perimeter × ceiling height = gross wall area.
- Subtract openings. Take off about 21 sq ft per door and 15 sq ft per window.
- Add the ceiling if you're painting it. Ceiling area = length × width.
- Divide by coverage, multiply by coats. Then round up to the nearest quart.
Worked example: a 12 × 14 ft room with 8 ft ceilings is (12 + 14 + 12 + 14) × 8 = 416 sq ft. Minus one door and two windows (about 51 sq ft) leaves 365 sq ft. Two coats ÷ 375 sq ft/gal = roughly 2 gallons.
Paint needed by room size (2 coats)
| Room size | Wall area | Paint (2 coats) |
|---|---|---|
| 10 × 10 ft | ~285 sq ft | 2 gallons |
| 12 × 12 ft | ~350 sq ft | 2 gallons |
| 12 × 14 ft | ~365 sq ft | 2 gallons |
| 14 × 16 ft | ~445 sq ft | 2 gal + 2 qt |
| 16 × 20 ft | ~525 sq ft | 3 gallons |
| 20 × 20 ft | ~590 sq ft | 3 gal + 1 qt |
When to add extra paint
- Rough or textured surfaces: add about 20% — knockdown, stucco, and brick drink more paint.
- Bare or first-time surfaces: add about 30% — new drywall and raw wood soak up the first coat.
- Big color changes: dark-over-light or vivid reds and yellows often need a third coat.
- Touch-ups: keep a quart in reserve rather than running short mid-wall.
How to calculate the cost to paint
Cost is just gallons × price per gallon, plus supplies and (if you hire out) labor. Interior wall paint runs about $26 a gallon at the budget end to $70+ for ultra-premium, so the brand you pick in the builder moves the bill more than anything else.
Doing it yourself, a typical room is $50 to $150 in paint and supplies. Hiring a pro adds labor, which is 70 to 85 percent of the total — a 2,000 sq ft home is roughly $700 to $1,800 DIY versus $3,000 to $7,500 hired. Tick "Add labor" above for a quick pro estimate, or use thecost calculator for a regional breakdown.