How to measure walls for paint
Last reviewed: November 2, 2026
Add up the width of every wall, multiply by the wall height, then subtract the area of anything you won't paint. In a rectangular room the walls total 2 × (length + width) × height.
You only need a tape measure and something to write on. Paint makers describe the same approach: Dulux’s UK guide, for example, multiplies height by width for each surface, then subtracts the openings.
Step 1: measure the room
Measure the length and width of the room along the walls, and the height from floor to ceiling. If the walls are uneven, use the largest figure. Rounding up here costs you a little extra paint, and rounding down could leave you short.
Step 2: work out the wall area
For a room of 14 ft × 12 ft with walls 8 ft high:
2 × (14 + 12) × 8 = 416 sq ft
In metric, for a room of 4.2 m × 3.6 m with walls 2.4 m high:
2 × (4.2 + 3.6) × 2.4 = 37.44 m²
Step 3: deduct what you won’t paint
Measure each door and window, and multiply its width by its height. Measure your own: sizes vary, and a fixed “standard door” figure is only a guess.
| Item | US example | Metric example |
|---|---|---|
| Door | 3 × 7 = 21 sq ft | 0.8 × 2.0 = 1.60 m² |
| Window | 4 × 4 = 16 sq ft | 1.2 × 1.2 = 1.44 m² |
| Total deducted | 37 sq ft | 3.04 m² |
| Wall area to paint | 379 sq ft | 34.40 m² |
Also deduct anything fixed to the wall that you’ll paint around, such as built-in cabinets. If you’re painting a door in the same paint, don’t deduct it.
Bump-outs and alcoves
A room with a bump-out, alcove, or fireplace surround has more wall than its length and width suggest, because the wall folds in and out. Measure each flat section as its own wall. The calculator’s Wall by wall option lets you enter every section with its own width and height.
Sloped walls
The calculator doesn’t handle sloped walls directly. For a triangular section under a sloping ceiling, the area is half the base × the height. To enter one as a wall, use half its base as the width. This works for simple triangles only, so for anything more complex, split the wall into shapes and check the sum by hand.
Baseboards and trim
The formula counts the wall from floor to ceiling, so it slightly overstates the area where baseboards and trim sit. It doesn’t calculate paint for the trim itself.