Every room here has 8 ft walls, one door and one window. There's a table for 4 × 8 sheets and one for 4 × 12. Read the first column if you're only doing the walls. Read the second if you're doing the ceiling too.
4 × 8 sheets
| Room | Walls only | Walls + ceiling |
|---|---|---|
| 10 × 10 ft | 10 | 14 |
| 10 × 12 ft | 11 | 16 |
| 12 × 12 ft | 13 | 18 |
| 12 × 14 ft | 14 | 19 |
| 14 × 16 ft | 16 | 24 |
| 16 × 20 ft | 19 | 30 |
4 × 12 sheets
| Room | Walls only | Walls + ceiling |
|---|---|---|
| 10 × 10 ft | 7 | 9 |
| 10 × 12 ft | 8 | 11 |
| 12 × 12 ft | 9 | 12 |
| 12 × 14 ft | 9 | 13 |
| 14 × 16 ft | 11 | 16 |
| 16 × 20 ft | 13 | 20 |
How this is worked out
Wall area is the distance around the room times the wall height. Every room here has 8 ft walls.
We take off 20 sq ft for the door and 12 sq ft for the window. Those are the allowances Handyman Calc uses. The ceiling is the room's length times its width.
Then we add 10% for cuts and waste. We divide by the area of one sheet and round up. A 4 × 8 sheet is 32 sq ft and a 4 × 12 is 48.
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There's a chart for how many bags of concrete for a slab too, and more on the Handyman Calc page.