How to measure a room for paint
Measure walls, openings and ceilings without confusing floor area with wall area.
Editorial review: October 11, 2026 · AI-assisted initial content · Editorial transparency
Measure the length of each wall and its painted height. For a rectangular room with a uniform height, measure length, width and height once: wall area = 2 × (length + width) × height.
A five-step measurement sheet
- Write the room name and the units at the top of your notes.
- Measure the room length and width along the walls.
- Measure from the top of the baseboard to the ceiling, or the actual upper paint line.
- Measure doors, windows and any other areas that will not receive this paint.
- Record the ceiling separately if it uses a different product or sheen.
Irregular rooms
Use one Individual wall entry per wall. Add alcoves as extra walls; do not treat an L-shaped room as one large rectangle. For a sloping or triangular section, calculate its area manually and enter Custom area. A triangle is base × height ÷ 2.
Feet and inches
12 ft 6 in is 12.5 ft, not 12.6 ft. You can instead select inches and enter 150. For metric measurements, 250 cm equals 2.5 m. The calculator converts existing dimensions when you switch units.
Common measurement error
A 12 × 10 ft floor is 120 sq ft, but its 8 ft high walls have 352 sq ft before openings. Using floor area would miss most of the surface.
A measurement worksheet
Copy these columns to paper for each surface. Keep dimensions and areas in one unit system throughout.
| Record | Metric example | Imperial example |
|---|---|---|
| Room length × width × height | 4 × 3 × 2.5 m | 12 × 10 × 8 ft |
| Gross walls | 35 m² | 352 sq ft |
| Openings | 1.8 + 1.2 = 3 m² | 21 + 24 = 45 sq ft |
| Net walls | 32 m² | 307 sq ft |
| Ceiling (separate finish) | 12 m² | 120 sq ft |
| Your measurements | Length ___ Width ___ Height ___ | Openings ___ Net area ___ |
These are two separate example rooms, not conversions of the same room. Use Room mode for a rectangle or individual walls for uneven heights. Use the ceiling calculator for flat ceilings.
Source notes
- Sherwin-Williams paint calculator — manufacturer planning guidance; check the specific product data sheet before buying.
- Benjamin Moore paint calculator — manufacturer estimating reference.
- Resene estimating worksheet — worked area and coverage methods.
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