🎨 Paint Calculator
Find out how much paint you need for a room from its size, number of doors and windows, and the number of coats.
Quick answer: Paint = (wall area − doors and windows) × coats ÷ coverage. A 12 × 12 ft room with 8 ft walls, one door and two windows has about 333 sq ft to paint; two coats at 350 sq ft per gallon need 1.9 gallons, so buy 2.
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Paint Calculator inputs
Result
Paint needed
1.9 gal
Buy 2 × 1-gallon cans
| Wall area | 384 sq ft |
| Doors & windows | −51 sq ft |
| Paintable area | 333 sq ft |
| Paint for 2 coats | 1.9 gal |
- Coverage used
- 350 sq ft/gal
- Total area painted
- 666 sq ft
How to estimate paint for a room
Measure the perimeter of the room, multiply by the wall height, subtract doors and windows, then multiply by the number of coats and divide by the coverage printed on the can.
Paint = [2 × (length + width) × height − openings] × coats ÷ coverage
Worked example
A 12 × 12 ft bedroom with 8 ft ceilings has 2 × (12 + 12) × 8 = 384 sq ft of wall. Subtract one door (21 sq ft) and two windows (2 × 15 = 30 sq ft) to get 333 sq ft. Two coats cover 666 sq ft; at 350 sq ft per gallon that is 1.9 gallons – buy 2 gallons.
Typical paint coverage
| Surface | Coverage per gallon | Per liter |
|---|---|---|
| Smooth, previously painted wall | 350–400 sq ft | 9–10 m² |
| New drywall / plaster (with primer) | 300–350 sq ft | 7–9 m² |
| Textured or rough surface | 250–300 sq ft | 6–7 m² |
| Ceiling paint | 350–400 sq ft | 9–10 m² |
Metric rooms
Switch the units to meters and the calculator uses 10 m² per liter and rounds up to 2.5-liter tins, the most common size outside the US. Enter your paint's exact coverage under advanced options if it differs.
Painting tips
- Prime new plaster, bare wood or dark colours before the top coat.
- Buy all the paint for a room at once so the colour matches exactly.
- Trim, doors and skirting boards use a different paint – about 1 quart covers trim in an average room.
- Stir well and box (mix together) cans when using more than one.
Frequently asked questions
How much area does a gallon of paint cover?
Most interior wall paints cover 350–400 sq ft per gallon (about 9–10 m² per liter) on smooth, primed walls. Rough, porous or textured surfaces can cut this to 250–300 sq ft.
Do I need two coats of paint?
Usually yes. Two coats give even colour and better durability, especially when changing colour. One coat may be enough when repainting the same colour with a high-quality paint.
How much do doors and windows reduce the area?
This calculator subtracts about 21 sq ft (1.95 m²) per standard door and 15 sq ft (1.39 m²) per window. Large patio doors or picture windows will remove more.
Should I buy extra paint?
The result is already rounded up to whole cans. Many painters keep a little left over for touch-ups – store it sealed and labelled with the room name.