1x3 actual size
¾ × 2½ inches
1.9 × 6.3 cm · 19 × 64 mm · sold as a 1x3
Nominal against actual
| Nominal | Actual | Difference | |
|---|---|---|---|
| Thickness | 1 in | ¾ in (19 mm) | −¼ in |
| Width | 3 in | 2½ in (64 mm) | −½ in |
| Cross-section | 3 in² | 1.88 in² | −38% |
What a 1x3 is for
Lath, bracing and light frames. It is the size most garden trellis and lightweight crating is built from.
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 1x3s are 7½ inches across, not 9; eight of them are 20 inches rather than 24, 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 |
| 1x4 | ¾ × 3½ in | 19 × 89 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 1x3?
¾ × 2½ inches — 1.9 × 6.3 cm, or 19 × 64 mm.
Why is a 1x3 not 1 by 3 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 1x3 than its name?
¼ inch off the thickness and ½ off the width, which is 38% 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 1x3 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.