Measure a room for paint, including doors and windows
Record wall dimensions and actual openings, keep ceiling area separate, and calculate a reproducible paintable area.
A floor measurement is not a wall measurement. Two rooms can have the same floor area but different perimeters and wall heights. Start with the surfaces that you intend to paint, then record the product that will be used on each surface.
Record the room shell
For a rectangular room, measure length, width and wall height in one consistent system. The wall-area model is 2 × (length + width) × height. This assumes four full rectangular walls of equal height. Measure sloping ceilings, partial-height walls and unusual shapes separately; the current tool does not model them.
Use the distance across the surface to be covered. A drawing is useful for recording measurements, but a decorative room illustration is not a scale drawing or a survey.
Subtract actual openings
Each opening deduction is width × height × quantity. Use the count only for openings with the same dimensions. Add another opening type when a window has a different size. Do not substitute an assumed standard door size for a measurement.
Door and window deductions apply to walls. They do not reduce ceiling area. If the openings exceed the gross wall area, stop and check units, counts and measurements. Turning a negative area into zero would conceal an input error.
A complete area example
Test room: 4 m long, 3 m wide, 2.5 m high.
Gross walls = 2 × (4 + 3) × 2.5 = 35 m².
One test opening 2 × 2 m = 4 m². Net walls = 31 m².
Ceiling, if included, adds 4 × 3 = 12 m² to its assigned product.
The 2 × 2 m opening is a calculation example, not a typical window recommendation. A wall-product estimate of 31 m² becomes 43 m² only when the ceiling uses that same assigned product. A different ceiling product remains separate.
Before using the estimate
- Confirm that the room is rectangular and the walls have one height.
- Use actual opening sizes and counts.
- Decide whether to paint the ceiling, and assign it explicitly.
- Choose coats and coverage from the product label, not from the room dimensions.
Enter the measurements in the paint calculator, then use the coverage and coats guide to turn area into volume.
Sources and scope
For definitions of wallpaper match, repeat and packaging, see Brewster's product properties and Graham & Brown's wallpaper FAQ. Product instructions take precedence over generic examples. Unit conversions use the exact international foot (0.3048 m) and US liquid gallon (3.785411784 L); see NIST conversion factors.