A common rule puts the top of the chair rail at about one third of the ceiling height. Tall wainscoting, often used with board and batten, sits nearer two thirds.
| Ceiling | Chair rail top (one third) | Tall wainscoting top (two thirds) |
|---|---|---|
| 8 ft | 32" | 64" |
| 9 ft | 36" | 72" |
| 10 ft | 40" | 80" |
| 12 ft | 48" | 96" |
Heights are to the top of the rail. Keep the rail clear of window sills where you can.
Working in millimetres? The wall panelling calculator works in mm and calls it a dado rail.