Estimating drywall for three walls, not four
Most calculators assume every wall is in the job. A renovation often is not — one wall has the wardrobe, the tile or the brick. Here is what that does to the numbers.
The problem with "room size" calculators
A calculator that takes length × width × height and multiplies the perimeter by the height counts all four walls. If you are leaving one wall alone, you buy that wall's drywall for nothing — and for a 12 × 9 ft wall that is 108 sq ft, or about four sheets with allowance.
Per-wall scope
Renovation Buy List generates each wall as its own surface. You tick the walls that are in the job. Unticked walls never enter the drywall total, and openings on them are ignored for that material. The same scope choice is made separately for paint and primer, so you can board three walls and paint four.
The numbers
| Scope (12 × 12 × 9 ft, door 3 × 7, window 4 × 4, flat ceiling, 10%, 4 × 8 sheets) | Net area | Basis | Sheets |
|---|---|---|---|
| Four walls + ceiling | 539 sq ft | 592.9 | 19 |
| Three walls + ceiling | 431 sq ft | 474.1 | 15 |
| Three walls, no ceiling | 287 sq ft | 315.7 | 10 |
| One wall (Wall A with the door) | 87 sq ft | 95.7 | 3 |
Where the openings go
An opening is attached to its host wall. If that wall is out of scope, the opening is out of scope too — it does not get subtracted from some other wall. This is why the planner asks which wall each door or window is on rather than taking a total opening area.
Ceiling as its own surface
The ceiling is listed separately in the breakdown even when you buy the same board, because ceiling board is often a different thickness and because the trace should show where each sheet goes. If you pool the purchase, rounding happens once on the combined basis.
Try it on the drywall calculator — untick a wall and watch the sheet count change — or plan the whole room in the planner.