Box widths for walls from 8 to 16 ft, with a 4" reveal at each end and 4" between boxes. With a 34" chair rail over a 5 1/4" baseboard, every box is 18 1/4" tall.
| Wall width | 2 boxes | 3 boxes | 4 boxes | 5 boxes |
|---|---|---|---|---|
| 8 ft | 42" | 26 5/8" | 19" | 14 3/8" |
| 10 ft | 54" | 34 5/8" | 25" | 19 1/4" |
| 12 ft | 66" | 42 5/8" | 31" | 24" |
| 14 ft | 78" | 50 5/8" | 37" | 28 3/4" |
| 16 ft | 90" | 58 5/8" | 43" | 33 5/8" |
Sizes are to the outside of the molding. Every box on a wall is the same width here; open a layout to widen the center box, change the reveal or add upper panels.