A 5/4 board is 1¼ inches thick (1.25").
A "5/4" (five-quarter) board is a nominal lumber size where 5/4" equals 1.25" actual thickness after drying and planing. This measurement is standard in rough-sawn lumber, though the final thickness may vary slightly (1.18"-1.25") depending on milling. Common uses include decking, outdoor furniture, and heavy-duty flooring.
Understanding 5/4 Lumber Dimensions
- Nominal size: "5/4" refers to the rough-cut thickness (1.25").
- Actual size: After planing, typically 1.18"-1.25" (varies by manufacturer).
- Width/length: Nominal widths (e.g., 5/4×6) refer to rough-cut dimensions; actual width is ~½" less (e.g., 5.5" for a "6" board).
- Comparison: Thicker than 1" (actual ¾") but thinner than 2" (actual 1½") lumber.
5/4 Board vs. Other Common Thicknesses
| Nominal Size | Actual Thickness | Common Uses | Weight (per sq. ft., approx.) |
|---|---|---|---|
| 1" (e.g., 1×6) | ¾" | Interior trim, shelving, light furniture | 1.5-2 lbs |
| 5/4" (e.g., 5/4×4) | 1.18"-1.25" | Decking, outdoor furniture, heavy flooring | 2.5-3.5 lbs |
| 2" (e.g., 2×4) | 1½" | Framing, structural supports, raised beds | 3-4 lbs |
When to Use 5/4 Boards
- Outdoor projects: Ideal for decking (resists warping better than 1" boards).
- High-traffic surfaces: Thicker than standard flooring; handles wear well.
- Furniture: Adds durability for benches, tables, or bed frames.
- Avoid for: Delicate woodworking (e.g., cabinetry) where thinner stock is preferred.
Buying Tips
- Check actual measurements: Confirm thickness at purchase (some suppliers plane to 1.18").
- Species matters: Hardwoods (e.g., oak) are denser than softwoods (e.g., pine) at the same thickness.
- Cost: Expect 20-30% more expense than 1" lumber due to material volume.
- Moisture content: Kiln-dried (under 19%) prevents shrinkage after installation.