Actual Lumber Sizes: Nominal vs Actual 2x4, 2x6, 1x6 and More
Lumber is smaller than its name. A 2×4 is really 1½ × 3½ inches, a 2×6 is 1½ × 5½ and a 1×6 is ¾ × 5½. The name is the nominal size, the size of the rough board at the sawmill; drying and planing leave the actual size. The chart below is for dry, surfaced softwood, the standard for building lumber in the United States. For the volume of a board in board feet, use the nominal size: a 2×4×8 is 5.33 board feet (see the board foot calculator).
Nominal and actual sizes
| Nominal size | Actual size (inches) | Actual (decimal) | Actual (mm) |
|---|---|---|---|
| 1 × 2 | ¾ × 1½ in | 0.750 × 1.500 in | 19 × 38 mm |
| 1 × 3 | ¾ × 2½ in | 0.750 × 2.500 in | 19 × 64 mm |
| 1 × 4 | ¾ × 3½ in | 0.750 × 3.500 in | 19 × 89 mm |
| 1 × 6 | ¾ × 5½ in | 0.750 × 5.500 in | 19 × 140 mm |
| 1 × 8 | ¾ × 7¼ in | 0.750 × 7.250 in | 19 × 184 mm |
| 1 × 10 | ¾ × 9¼ in | 0.750 × 9.250 in | 19 × 235 mm |
| 1 × 12 | ¾ × 11¼ in | 0.750 × 11.250 in | 19 × 286 mm |
| 2 × 2 | 1½ × 1½ in | 1.500 × 1.500 in | 38 × 38 mm |
| 2 × 3 | 1½ × 2½ in | 1.500 × 2.500 in | 38 × 64 mm |
| 2 × 4 | 1½ × 3½ in | 1.500 × 3.500 in | 38 × 89 mm |
| 2 × 6 | 1½ × 5½ in | 1.500 × 5.500 in | 38 × 140 mm |
| 2 × 8 | 1½ × 7¼ in | 1.500 × 7.250 in | 38 × 184 mm |
| 2 × 10 | 1½ × 9¼ in | 1.500 × 9.250 in | 38 × 235 mm |
| 2 × 12 | 1½ × 11¼ in | 1.500 × 11.250 in | 38 × 286 mm |
| 4 × 4 | 3½ × 3½ in | 3.500 × 3.500 in | 89 × 89 mm |
| 4 × 6 | 3½ × 5½ in | 3.500 × 5.500 in | 89 × 140 mm |
| 6 × 6 | 5½ × 5½ in | 5.500 × 5.500 in | 140 × 140 mm |
Why the difference matters
- Framing: a 2×4 wall is 3½ inches thick, and with ½ inch drywall on each side the finished wall is 4½ inches.
- Spans and fit: a cut-out, a notch or a hole for a joint has to match the actual size, not the name.
- Counting materials: the coverage of deck boards is the actual width. A 5/4×6 deck board is about 1 inch thick and 5½ inches wide, so with a gap it covers about 5¾ inches. See the deck board calculator.
- Studs: wall studs are spaced 16 or 24 inches on center, which the stud calculator counts.
Wall thickness
| Wall | Studs | With ½ in drywall on both sides |
|---|---|---|
| 2 × 4 stud wall | 3.5 in | 4.5 in |
| 2 × 6 stud wall | 5.5 in | 6.5 in |
Plywood and sheet goods
Sheets are also thinner than their name. The nominal thickness and the usual actual thickness of plywood and OSB:
| Nominal | Actual |
|---|---|
| 1/4 in | 7/32 in |
| 3/8 in | 11/32 in |
| 1/2 in | 15/32 in |
| 5/8 in | 19/32 in |
| 3/4 in | 23/32 in |
A sheet is 4 × 8 feet (48 × 96 inches), and is nominal in length and width. Check the thickness with calipers if it matters, because it varies by manufacturer.
Notes
- These actual sizes are for dry, surfaced softwood lumber. Rough-sawn lumber is closer to its nominal size, and some boards, such as hardwood or reclaimed wood, are not standard.
- Pressure-treated lumber is sometimes wet when you buy it and shrinks as it dries.
- Lumber is sold in lengths in 2 foot steps (8, 10, 12, 14 and 16 feet). Precut wall studs are shorter, 92⅝ inches, so that with three plates they make a wall for an 8 foot ceiling.
Frequently asked questions
What is the actual size of a 2x4?
A 2×4 is 1½ inches by 3½ inches (38 × 89 mm). It is called a 2×4 because it was cut to that size before it was dried and planed smooth.
What is the actual size of a 2x6?
A 2×6 is 1½ by 5½ inches (38 × 140 mm). A 2×8 is 1½ by 7¼, a 2×10 is 1½ by 9¼ and a 2×12 is 1½ by 11¼ inches.
What is the actual size of a 1x6?
A 1×6 is ¾ by 5½ inches (19 × 140 mm).
What is the actual size of a 4x4?
A 4×4 post is 3½ by 3½ inches (89 × 89 mm), and a 6×6 post is 5½ by 5½ inches.
Why is lumber smaller than its name?
The name is the size of the rough board when it was cut at the sawmill. Drying shrinks the board, and planing it smooth on all four sides takes off another quarter to half an inch from each dimension.
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Estimates only. Quantities depend on your materials, site and supplier. Confirm important numbers before you order, and follow local building codes for anything structural.