Room Paint Calculator
For a 12 × 12 ft room (48 ft of total wall perimeter) with an 8 ft ceiling, the total wall area is 48 × 8 = 384 sq ft. With two coats and a 10% touch-up allowance that comes to about 422 sq ft of coverage — 3 gallons, based on 350 sq ft of coverage per gallon for one coat (175 sq ft per gallon for two coats). Subtract door and window area from the total before you buy.
Reviewed by The ponderloop teamUpdated 2026-07-11How we calculate
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0 sq ft + 0% waste = 0 sq ft
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How this number is calculated
0 sq ft (no waste added) ÷ 175 sq ft per gallon = 0 gallons
Shopping list
- Interior wall paint (1 gallon)
- Paint roller kit (roller, tray, covers)
- Angled sash paintbrush (2.5 inch)
- Painter's tape
- Canvas drop cloth
- Paint tray liners
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Methodology & assumptions
Total wall area is the room's total wall perimeter (2 x (length + width) for a rectangular room) times ceiling height, minus any door/window openings. That area is divided by coverage per gallon — a 350 sq ft/gal baseline for one coat of interior latex, halved for the standard two-coat full-room repaint — then multiplied by your chosen waste percentage and rounded up to the next whole gallon.
- Manufacturer coverage specs (~350 sq ft/gal, one coat, interior latex)
- Typical US interior wall paint retail price range, 2026
Worked examples
| Room | Result |
|---|---|
| 12 × 12 ft room (48 ft perimeter), 8 ft ceiling, 2 coats, +10% waste | 384 sq ft + 10% waste ≈ 422.4 sq ft → 3 gallons |
| 14 × 14 ft room (56 ft perimeter), 9 ft ceiling, 2 coats, exact | 504 sq ft, exact (0% waste) → 3 gallons |
| 10 × 10 ft room (40 ft perimeter), 8 ft ceiling, 1 coat, +10% waste | 320 sq ft + 10% waste ≈ 352 sq ft → 2 gallons |
Frequently asked questions
- What do I enter for "total wall perimeter"?
- Add up the length of every wall in the room. For a rectangular room that is simply 2 x (room length + room width) — a 12 x 12 ft room has a perimeter of 2 x (12 + 12) = 48 ft. For an irregular room, add each wall segment individually.
- How many gallons of paint do I need for a whole room?
- Multiply the total wall perimeter by the ceiling height to get total wall area, subtract the area of doors and windows, then divide by the coverage per gallon for your number of coats. One coat covers about 350 sq ft per gallon; two coats (the standard for a full room) effectively halves that to about 175 sq ft per gallon.
- Does this include the ceiling?
- No — this calculator covers the four walls only. Use a dedicated ceiling paint calculator for the ceiling, since ceiling (flat) paint is usually a different product from wall paint and is bought separately.
- What surfaces or color changes need more paint than the 350 sq ft/gal baseline?
- Rough, textured, or porous walls (unprimed drywall, stucco, heavily patched areas) soak up more paint per sq ft than the 350 sq ft/gal baseline assumes. Going from a dark existing wall color to a much lighter one, or light to a saturated dark color, often needs a third coat to fully hide the old color — bump the Coats field up if that applies to your room.
- Should I round up or buy an extra gallon for a full room?
- Always round up to the next full gallon, and consider one spare can for touch-ups after furniture goes back in. Paint batches are tinted together, so a rushed extra can weeks later may not match exactly.