Areas
Room wall and ceiling area less doors and windows
- where
- room perimeter (m)
- room length (m)
- room width (m)
- gross wall area (m²)
- wall height (m)
- net wall area (m²)
- total area of doors and windows (m²)
- ceiling area (m²)
- include the ceiling (1 yes, 0 no)
- total area to paint (m²)
Explain this equation
Works out the wall and ceiling area of a rectangular room, less doors and windows. It is the starting point for paint and paper quantities.
The perimeter is twice length plus width. Times the wall height it gives the gross wall area. Take off the doors and windows for the net wall area. The ceiling is length times width; C is a switch, 1 to include it and 0 to leave it out.
Areas of rectangles, added and subtracted.
Sense check: a 4.2 × 3.6 m room with 2.4 m walls has about 37.4 m² of gross wall; with 3 m² of openings and the ceiling, about 49.6 m² to paint.
Watch out: chimney breasts, alcoves and bay windows add wall area; measure them in.
Works out the wall and ceiling area of a rectangular room for paint or paper, less doors and windows.
Enter your values to see the result.
Good to know
Measure wall face to wall face. A standard 1981 × 762 mm door opening is about 1.5 m²; measure windows on the wall face. For emulsion, measure walls from the top of the skirting if the skirting is being glossed separately. Reveals are extra surface: add depth × perimeter of each opening.
Common mistake
Deducting openings for wallpaper as if paper were paint. For paper, the drop count by perimeter is safer (see the wallpaper roll calculator), because offcuts above doors and windows rarely save a whole drop.
Limits
Rectangular rooms with flat ceilings. Measure chimney breasts, alcoves, bays and sloping ceilings separately and add them.
Sources
- Geometry: rectangle and cylinder surface areas, prism volumes
- Farrow & Ball, How much paint do I need? (coverage per tin, e.g. Estate Emulsion 70 m² per 5 L; Masonry & Plaster Stabilising Primer 100 m² per 5 L; one primer & undercoat plus two topcoats)
- Howarth Timber, UK door sizes (imperial 1981 × 762 × 35 mm; metric 2040 mm high, 40 mm thick)
Results are calculations from the published methods and figures shown, and depend on the data you enter. Coverage depends on the product, surface and application. Always follow the paint and wallcovering manufacturers’ data sheets and BS 6150 / BS 8000-12. Check prices and VAT with your own records and HMRC.