A 5/4×4 is sold and labeled as 5/4×4, but it actually measures 1" × 3½". The difference comes from milling and drying — the board starts closer to its named size, then shrinks as it's surfaced smooth and dried to standard moisture content.
Narrow decking runs, deck stair treads
5/4 decking is milled with eased (rounded) edges on both long sides, unlike standard 2-by lumber — that rounded edge is a deck-specific detail, not a defect.
| Nominal Size | Actual Size | Actual (decimal) |
|---|