Paint calculator
Enter the room size and openings. Coverage defaults to 350 sq ft per gallon; use the figure on your can, since it varies by product and surface.
Materials takeoff
Paint Calculator · https://estimahome.com/paint-calculator/
Room length: 12 ftRoom width: 12 ftWall height: 8 ftDoors: 1 eaWindows: 2 ea
- Wall area
- 333 sq ft
- Ceiling
- Not included
- Paint needed
- 1.9 gal
- Buy
- 2 gal
| No. | Item | Qty | Unit | Unit cost | Amount |
|---|---|---|---|---|---|
| 1 | Paint, 2 coats | 2 | gal | $42.00 | $84.00 |
| 2 | Rollers, brushes, tape, tray | 1 | set | $35.00 | $35.00 |
- Subtotal
- $119.00
- Likely range
- $101.15 – $136.85
- Ceilings usually take a flat ceiling paint; it is priced here at the wall-paint price.
- Big color changes, bare drywall and rough texture can need an extra coat.
Buy these materials
- 2 gallons of interior paintAmazon search for gallons of interior paint (opens in new tab)
- 1 paint roller kitAmazon search for paint roller kit (opens in new tab)
Links open a store search for each item. Check sizes and grades against your plan.
Quick reference
- Wall area of a rectangular room = 2 × (length + width) × height.
- A 12 × 12 ft room with 8 ft walls, one door and two windows has 333 sq ft of paintable wall.
- Two coats on that room take 1.9 gal at 350 sq ft per gallon.
How it's calculated
⌈x⌉ means round up to the next whole unit; ⌊x⌋ means round down. Every quantity you buy is rounded up.
Wall area = 2 × (length + width) × height − doors × door area − windows × window areaCeiling area = length × widthPaint (gal) = (wall area + ceiling area) × coats ÷ coverageGallons to buy = ⌈ paint gallons ⌉Primer (gal) = ⌈ (wall area + ceiling area) ÷ primer coverage ⌉Cost = Σ (quantity × unit price); range = cost × (1 ± range % ÷ 100)
Worked example
A 12 × 12 ft room with 8 ft walls has 2 × (12 + 12) × 8 = 384 sq ft of wall. Less 1 door at 21 sq ft and 2 windows at 15 sq ft leaves 333 sq ft. Two coats at 350 sq ft per gallon: 333 × 2 ÷ 350 = 1.9 gal, so buy 2. Paint and supplies at the default prices: $119.00.
Questions
How much paint for a 12 × 12 room?
With 8 ft walls, one door and two windows, about 333 sq ft of wall. Two coats is about 1.9 gal, so 2 gallons.
How much does a gallon of paint cover?
Most interior wall paint lists 250 to 400 sq ft per gallon. Rough or porous surfaces use more.
Do I need primer?
On new drywall, patched areas, stains, and big color changes, yes. On clean, previously painted walls in a similar color, usually not.
Cite: “Paint Calculator.” EstimaHome, https://estimahome.com/paint-calculator/. Updated 2026-10-20. Formulas in machine-readable form: /api/calculators.json.