How to Calculate Wall Area With Doors and Windows

To calculate wall area, measure the length and height of each section, add the rectangles and subtract doors or windows only when those surfaces will not receive the same finish. Treat niches, reveals and projections separately because their faces may need material too.

The basic calculation for a simple room

For each wall, multiply length by height, then add the wall areas. A rectangular room can often be calculated from its perimeter, but separate measurements are safer when heights, niches or projections differ.

When to subtract doors and windows

• Record the width and height of each repeated opening and multiply one opening area by its count.
• Subtract an opening only from a surface that will genuinely remain unfinished with the material being estimated.
• Do not forget reveals, lintels or side faces if they will be painted, plastered, wallpapered or tiled.
• If an opening is covered by cuts or the finish continues into its sides, do not remove it automatically.

Niches, columns and projections

Split a complicated wall into simple planes. Include the faces of a niche that will be finished, and include the ends of a projection. For curved or irregular areas, take several practical measurements and keep a separate allowance for cutting and application losses.

Using the wall area calculator

The Wall Area Calculator is useful for a rectangular room with repeated doors and windows. For an irregular plan, calculate zones separately and use the combined result in the Paint, Plaster, Wall Filler or Wallpaper Calculator.

Check the measurements before buying

• Compare wall lengths at the floor and ceiling; a difference may reveal a sloping or irregular geometry.
• Mark surfaces covered by fitted furniture, panels or another finish.
• Keep the sketch with the original measurements, not only the final total.
• Take product coverage and application losses from the material instructions separately from the area calculation.