How to estimate paint for a room
Paint is sold by the gallon, but you buy coverage for wall area × coats. Skipping the math leads to mid-project store runs or leftover gallons you cannot return once tinted.
- Find wall area: perimeter × ceiling height.
- Subtract doors (~20 sq ft each) and windows (~15 sq ft each).
- Add ceiling (length × width) if you are painting it too.
- Multiply by number of coats.
- Divide by coverage per gallon on the paint can.
This calculator uses industry-average deductions — measure your openings if you want precision.
Worked example: 14×12 ft room, 8 ft ceilings
- Perimeter: 2 × (14 + 12) = 52 ft
- Wall area: 52 × 8 = 416 sq ft
- Minus 2 doors (40) and 2 windows (30): 346 sq ft paintable
- Two coats: 692 sq ft total coverage needed
- At 350 sq ft/gal: 692 ÷ 350 = 1.98 → buy 2 gallons (walls only, no ceiling)
Toggle Include ceiling in the calculator if you are painting the fifth wall — that adds length × width to the total.
Coverage guidelines
| Surface | Typical coverage |
|---|---|
| Smooth previously painted wall | 350–400 sq ft/gal |
| Textured or porous drywall | 250–350 sq ft/gal |
| Dramatic color change | Plan 2 coats minimum |
| Dark over light (or reverse) | 2 coats + primer |
Always read the can. Premium paints and flat finishes spread differently than builder-grade eggshell.
Primer is not included here
New drywall, stains, or dark-to-light jumps often need primer first — buy primer separately; this estimate is for finish coats only.
Common primer scenarios:
- New drywall — one coat primer before color
- Stains / smoke / water marks — stain-blocking primer
- Bold color changes — tinted primer reduces topcoat count
Primer coverage is often 200–300 sq ft/gal — do not assume it matches finish paint.
Trim, doors, and cabinets
This tool estimates main wall fields. Trim, doors, and cabinets are usually calculated separately:
- Trim: measure linear feet × height of base + casing; often 1–2 quarts per average room
- Doors: one door face ≈ 20 sq ft both sides if painting slab doors
- Ceilings: enable the ceiling toggle or add length × width manually
Buying strategy
- Custom tints: buy an extra quart for touch-ups — batch drift is real
- One-gallon vs five-gallon: five-gallon pails save money on whole-house jobs if color is locked
- Spray vs roll: sprayers use more paint through overspray — add 10% if spraying
Drywall project next?
If you are finishing new walls before paint, estimate sheets with our drywall calculator — hang, tape, and prime before you buy finish color.
Paint or wallpaper?
For accent walls and pattern, compare paint vs wallpaper — then use this calculator if paint wins.