Actual lumber size calculator (nominal to actual)
A 2×4 is not 2 by 4 inches. Pick a nominal size (the name on the tag) to see its actual size, board feet and true volume.
Enter your measurements
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- Actual thickness (decimal)
- 1.5 in
- Actual width (decimal)
- 3.5 in
- Board feet (nominal — what a board-foot price is charged on)
- 5.33 board feet
- Board feet (actual volume)
- 3.5 board feet
- Wood you get vs. what you pay for (if priced by the board foot)
- 66%
- Actual volume
- 0.292 cu ft
Nominal 2×4 → dressed dry to 1-1/2 × 3-1/2 in (PS 20 standard sizes)
Billed: 2 × 4 × 8 ft ÷ 12 = 5.33 board feet · Actual: 1.5 × 3.5 × 8 ft ÷ 12 = 3.5 board feet (66%)
- Green (unseasoned) and rough-sawn lumber is larger than these dry, surfaced sizes. Pressure-treated lumber is often sold wet and shrinks slightly as it dries.
Quick answers for common sizes
| Example | Answer |
|---|---|
| What is the actual size of a 2x4 | 1-1/2 × 3-1/2 in |
| What is the actual size of a 4x4 | 3-1/2 × 3-1/2 in |
| What is the actual size of a 2x6 | 1-1/2 × 5-1/2 in |
Nominal vs actual size, board feet at the length above
| Nominal size | Actual size (what your tape reads) | Board feet (nominal — what a board-foot price is charged on) | Board feet (actual volume) |
|---|---|---|---|
| 1×4 | 3/4 × 3-1/2 in | 2.67 board feet | 1.75 board feet |
| 1×6 | 3/4 × 5-1/2 in | 4 board feet | 2.75 board feet |
| 2×4 | 1-1/2 × 3-1/2 in | 5.33 board feet | 3.5 board feet |
| 2×6 | 1-1/2 × 5-1/2 in | 8 board feet | 5.5 board feet |
| 2×8 | 1-1/2 × 7-1/4 in | 10.67 board feet | 7.25 board feet |
| 2×10 | 1-1/2 × 9-1/4 in | 13.33 board feet | 9.25 board feet |
| 2×12 | 1-1/2 × 11-1/4 in | 16 board feet | 11.25 board feet |
| 4×4 | 3-1/2 × 3-1/2 in | 10.67 board feet | 8.17 board feet |
| 6×6 | 5-1/2 × 5-1/2 in | 24 board feet | 20.17 board feet |
| 4/4 hardwood | 13/16 × 6 in (S2S) | 4 board feet | 3.25 board feet |
| 8/4 hardwood | 1-3/4 × 6 in (S2S) | 8 board feet | 7 board feet |
Dry, surfaced softwood lumber in the US and Canada is dressed to standard actual sizes. The board feet are what you are billed for; the true volume is what you get. Hardwood quarters (4/4 to 12/4) show the standard surfaced thickness. New to this? Words explained.
Why nominal and actual sizes differ
Nominal size is roughly the size a board is sawn at while green. Drying shrinks it, and planing (surfacing) the four faces smooth takes a little more off. The finished, dry size is set by the American Softwood Lumber Standard (NIST PS 20), which is why a 2×4 from any US or Canadian mill measures 1½ × 3½ in.
| Nominal | Actual (in) | Actual (mm) |
|---|---|---|
| 1×2 | ¾ × 1½ | 19 × 38 |
| 1×4 | ¾ × 3½ | 19 × 89 |
| 1×6 | ¾ × 5½ | 19 × 140 |
| 1×8 | ¾ × 7¼ | 19 × 184 |
| 1×12 | ¾ × 11¼ | 19 × 286 |
| 2×4 | 1½ × 3½ | 38 × 89 |
| 2×6 | 1½ × 5½ | 38 × 140 |
| 2×8 | 1½ × 7¼ | 38 × 184 |
| 2×10 | 1½ × 9¼ | 38 × 235 |
| 2×12 | 1½ × 11¼ | 38 × 286 |
| 4×4 | 3½ × 3½ | 89 × 89 |
| 4×6 | 3½ × 5½ | 89 × 140 |
| 4×8 | 3½ × 7¼ | 89 × 184 |
The pattern is simple: up to 6 in nominal, subtract ½ in (¼ in for 1× thickness); from 8 in up, subtract ¾ in. Timbers — 5 in and thicker, such as 6×6 and 6×8 posts and beams — are usually dressed green instead, ½ in under nominal on each face, so a 6×6 is 5½ × 5½ in and a 6×8 is 5½ × 7½ in until it dries and shrinks a little.
Hardwood: quarters, surfaced two sides
Hardwood is sold by rough thickness in quarter inches and random width, not by nominal size. When the yard planes both faces (S2S), the National Hardwood Lumber Association rules set the standard finished thickness: 3/16 in comes off rough stock up to 1½ in, and ¼ in off thicker stock. Board feet stay on the rough thickness.
| Quarter | Rough | Standard S2S |
|---|---|---|
| 4/4 | 1 in | 13/16 in |
| 5/4 | 1¼ in | 1-1/16 in |
| 6/4 | 1½ in | 1-5/16 in |
| 8/4 | 2 in | 1¾ in |
| 12/4 | 3 in | 2¾ in |
The three sizes people ask about most each have a worked page: what is the actual size of a 2x4 (studs and wall depth), what is the actual size of a 2x6 (decking and 2×6 walls) and what is the actual size of a 4x4 (posts, wet and dry).
Nominal board feet vs actual volume
Lumberyards bill softwood by nominal board feet, so a 2×4×8 is priced as 5.33 board feet even though it holds only 3.5 board feet of wood. Use actual volume when you need weight, shipping, or a comparison with metric timber that is sold at its true size.
Metric timber
In the UK, Europe and Australia, timber is usually sold at its actual (or “finished”) size in millimetres — 45 × 95 mm, 18 × 144 mm and so on. Sawn sizes there are nominal in the same sense as US lumber, but planed timber is labelled with the size you actually get. Always check the label or measure.
What you’ll need
- 25 ft tape measureBudget price
A 25 ft tape with a stiff blade and a readable 1/16 in scale covers everything from cut lists to deck layout.
See options on Amazon (opens in a new tab) - Digital calipersBudget price
For measuring actual board and plywood thickness to the thousandth — useful for sizing dadoes and checking planed stock.
See options on Amazon (opens in a new tab) - Speed square (7 in)Budget price
Marks square and angled crosscuts and doubles as a saw guide for a circular saw. The degree scale is handy for rafters and stair angles.
See options on Amazon (opens in a new tab)
As an Amazon Associate we earn from qualifying purchases. Links to products are affiliate links — they cost you nothing extra and help keep these calculators free.
Frequently asked questions
What is the actual size of a 2×4?
1½ × 3½ in (about 38 × 89 mm) dry and surfaced — more on what is the actual size of a 2x4.
What is the actual size of a 4×4?
3½ × 3½ in (about 89 × 89 mm) dry; wet treated posts can run slightly bigger. See what is the actual size of a 4x4.
What is the actual size of a 2×6?
1½ × 5½ in (about 38 × 140 mm) — see what is the actual size of a 2x6.
How thick is 8/4 hardwood once it is surfaced?
1¾ in under the NHLA standard surfaced (S2S) thicknesses — ¼ in comes off 2 in rough stock. A cupped or twisted board may need more taken off to flatten it, so buy 10/4 or 12/4 if a part must finish at a full 1¾ in.
Why is a 1×4 only ¾ in thick?
Boards are sawn near nominal size when green, then shrink as they dry and lose more to planing. The PS 20 standard sets the finished thickness of 1× boards at ¾ in.
Related guides
Sources
- NIST, Voluntary Product Standard PS 20-20, American Softwood Lumber Standard (Rev. 1, 2021) (opens in a new tab) — Table 3: minimum dry and green dressed sizes of boards, dimension and timbers (timbers 5 in and thicker: 1/2 in under nominal, green).
- National Hardwood Lumber Association, Rules for the Measurement & Inspection of Hardwood & Cypress (2019) (opens in a new tab) — Paragraph 14: standard surfaced (S2S) thicknesses — 4/4 to 13/16 in, 5/4 to 1-1/16, 6/4 to 1-5/16, 8/4 to 1-3/4, 12/4 to 2-3/4.
- American Hardwood Export Council, The Illustrated Guide to American Hardwood Lumber Grades (opens in a new tab) — Rough quarter thicknesses and the 3/16 in / 1/4 in surfacing allowance.
- NELMA, Standard Grading Rules, Section 4: Other Board Grades (2024) (opens in a new tab) — Standard Shop thicknesses: 5/4 surfaced to 1-5/32 in.