1x4 actual size
¾ × 3½ inches
1.9 × 8.9 cm · 19 × 89 mm · sold as a 1x4
Nominal against actual
| Nominal | Actual | Difference | |
|---|---|---|---|
| Thickness | 1 in | ¾ in (19 mm) | −¼ in |
| Width | 4 in | 3½ in (89 mm) | −½ in |
| Cross-section | 4 in² | 2.63 in² | −34% |
What a 1x4 is for
Trim, fencing rails and the face of a shelf. A 1x4 laid flat is the standard picket width in North America.
The name is the rough-sawn size before drying and planing. Why every board is smaller than its name →
What this costs you in practice
The error compounds wherever boards sit side by side. Three 1x4s are 10½ inches across, not 12; eight of them are 28 inches rather than 32, which is 4 inches short over a run you might have measured on paper. That is why framing is dimensioned centre to centre and not edge to edge: 16 inches on centre is a real 16 inches whatever the boards themselves measure, so a sheet of plywood still lands on a stud.
Other 1-inch nominal boards
| Nominal | Actual | In mm |
|---|---|---|
| 1x2 | ¾ × 1½ in | 19 × 38 mm |
| 1x3 | ¾ × 2½ in | 19 × 64 mm |
| 1x6 | ¾ × 5½ in | 19 × 140 mm |
| 1x8 | ¾ × 7¼ in | 19 × 184 mm |
| 1x10 | ¾ × 9¼ in | 19 × 235 mm |
| 1x12 | ¾ × 11¼ in | 19 × 286 mm |
Frequently asked questions
What is the actual size of a 1x4?
¾ × 3½ inches — 1.9 × 8.9 cm, or 19 × 89 mm.
Why is a 1x4 not 1 by 4 inches?
Because it was, once. The board is sawn at roughly its nominal size while green, then dried and planed smooth on all four faces, and both processes take material off. The name records the rough-sawn size and the label never caught up. This is standardised, not accidental — every mill in North America surfaces to the same finished dimensions.
How much smaller is a 1x4 than its name?
¼ inch off the thickness and ½ off the width, which is 34% less cross-section than the name implies. That matters for spans and for anything where you are counting boards to fill a width.
What lengths does a 1x4 come in?
Typically 6, 8, 10, 12, 14, 16, 20 feet. Unlike the cross-section, length is not reduced — an 8-foot board is 8 feet, or a little over, because it is cut to length after planing.