How much paint do I need?
Enter your room size or wall area, coats, and openings to get the gallons of paint you need and the cost. Brand-neutral coverage rates, free, no signup.
Short answer
To estimate paint, take the wall area (perimeter × ceiling height), subtract ~21 sq ft per door and 15 per window, multiply by coats, and divide by ~375 sq ft per gallon. A 12×12 room at two coats needs about 2 gallons. A gallon covers 350–400 sq ft per coat; deep colors and bare drywall need more.
Coverage
350–400
sqft/gal/coat
Door
−21 sq ft
opening
Window
−15 sq ft
opening
12×12 room
~2 gal
two coats
Paint coverage & cost by quality (2026)
| Quality | Coverage per gallon | Price per gallon | 12×12 room · 2 coats |
|---|---|---|---|
| Economy | 350 sq ft | $20–$30 | 2 gal · $40–$60 |
| Standard | 375 sq ft | $30–$45 | 2 gal · $60–$90 |
| Premium | 400 sq ft | $45–$70 | 2 gal · $90–$140 |
Paint cost only (no labor), one coat coverage per manufacturer specs. The 12×12 example assumes 8-ft ceilings, one door, and one window. Textured or unprimed walls absorb more paint.
Paint by room size
How we calculate this
Every number on this page comes from the same formulas the calculator runs — the standard coverage math printed on the paint can, not a brand promotion:
- Wall area. room perimeter × ceiling height: 2 × (length + width) × height. A 12×12 room with 8-ft ceilings has 384 sq ft of wall.
- Openings. subtract 21 sq ft per door and 15 sq ft per window — you don't paint them.
- Coverage needed. paintable area × number of coats (two coats is the norm for a color change).
- Gallons. coverage needed ÷ the paint's coverage per gallon (350–400 sq ft depending on quality), rounded up to whole gallons.
- Cost. gallons × the quality's typical price per gallon.
Assumptions
- Smooth, primed walls — rough or porous surfaces reduce coverage per gallon.
- Two coats for a typical repaint; drastic color changes may need a third.
- Paint cost only — professional labor typically adds $2–$6 per sq ft (validate locally).
Sources
Last reviewed: July 13, 2026
Related tools
Frequently asked questions
How much paint do I need?
Measure the wall area (perimeter × ceiling height), subtract about 21 sq ft per door and 15 per window, multiply by the number of coats, then divide by ~375 sq ft per gallon. A 12×12 room at two coats needs about 2 gallons. Enter your room above for an exact figure.
How many square feet does a gallon of paint cover?
About 350–400 square feet per coat for typical interior wall paint. Economy paint covers around 350, premium around 400. Deep colors, rough textures, and unprimed drywall reduce coverage.
How much paint for a 12x12 room?
A 12×12 room with an 8-foot ceiling has about 384 sq ft of wall. After a door and two windows and at two coats, that is roughly 2 gallons. The calculator adjusts for your exact openings and coats.
Do I need primer?
Prime bare drywall, patched areas, stains, or big color changes (like dark to light). Over an existing painted wall in a similar color, a good self-priming paint usually skips it. Primer is a separate product from your finish coats.