Paint calculator
Wall and ceiling area from room dimensions, minus openings, converted into gallons for one, two or three coats.
- Paintable area
- — ft²
- Gallons to buy
- —
- Estimated cost
- —
How the calculation works
Wall area = 2 × (length + width) × wall height
Subtract 21 ft² per door and 15 ft² per window. Add length × width if the ceiling is included. Multiply by the number of coats, then divide by 350 ft² per gallon:
gallons = area × coats ÷ 350
350 is the conservative figure. Most premium interior paints claim 375–400 ft² per gallon on a smooth, primed surface; bare drywall, texture and deep color changes eat the difference.
Worked example
A 12 × 10 ft room with 8 ft walls: perimeter is 44 ft, so 44 × 8 = 352 ft². One door (21) and two windows (30) remove 51 ft², leaving 301 ft². Two coats is 602 ft². 602 ÷ 350 = 1.72, so buy 2 gallons.
Coverage reference
| Surface | Coverage per gallon | Note |
|---|---|---|
| Primed drywall, flat | 375–400 ft² | Best case |
| Bare drywall | 300–350 ft² | Absorbs first coat |
| Textured / orange peel | 275–325 ft² | More surface area |
| Brick or masonry | 200–300 ft² | Highly variable |
Frequently asked
Do I need primer plus two coats?
New drywall, patched walls and drastic color changes need primer. Otherwise a paint-and-primer product with two coats is usually enough.
Should I round up or down?
Up. Paint mixed in one batch matches; buying a second gallon later can be a visible difference on the same wall.
Does the ceiling count as a wall?
No — it is a separate area and usually a separate product. Use the ceiling toggle above and add it explicitly.