REFERENCE TABLE #96 · CONSTRUCTION · MATERIALS
A 2×4 is not 2 by 4 inches — it is 1.5 × 3.5 inches after drying and planing. This chart gives every common size from 1×2 to 6×6, with actual dimensions, cross-section areas, and a board-foot calculator: a 2×4 × 8 ft is 5.33 board feet. Look a size up below and stop guessing at the yard.
Pick the stamped (nominal) size and a length. The calculator returns the dressed (actual) size, the board feet from nominal size, and the actual cross-section area. Rule: 1-inch boards finish at 0.75 inch; 2–6 inch dimensions lose 1/2 inch; dimensions over 6 inches lose 3/4 inch.
Because the name is the size before the board is finished. A rough-sawn 2×4 really is about 2 by 4 inches, but then it is dried and planed smooth on all four sides — a process called surfacing or dressing — and that shaves material off every face. The finished, dressed size is what you buy, and it is what fits in your wall. The rule for dressed lumber in North America: a 1-inch nominal board finishes at 3/4 inch thick; nominal dimensions from 2 through 6 inches lose 1/2 inch; any dimension over 6 inches loses 3/4 inch. So a 2×4 is 1.5 × 3.5, a 2×10 is 1.5 × 9.25, and a 6×6 post is 5.5 × 5.5. The shrinkage is not a defect and not a scam — it is the standard, and every span table, framing guide, and building code assumes the actual size.
Every row below follows the rule above, dimension by dimension. Print this table and take it to the yard — or use the lookup tool above for one size at a time, with board feet included.
| Nominal size | Actual size | Cross-section area | How it shrinks |
|---|---|---|---|
| 1×2 | 0.75 × 1.5 in | 1.12 sq in | Nominal 1 in loses 0.25 in; nominal 2 in loses 0.5 in. |
| 1×3 | 0.75 × 2.5 in | 1.88 sq in | Nominal 1 in loses 0.25 in; nominal 3 in loses 0.5 in. |
| 1×4 | 0.75 × 3.5 in | 2.62 sq in | Nominal 1 in loses 0.25 in; nominal 4 in loses 0.5 in. |
| 1×6 | 0.75 × 5.5 in | 4.12 sq in | Nominal 1 in loses 0.25 in; nominal 6 in loses 0.5 in. |
| 1×8 | 0.75 × 7.25 in | 5.44 sq in | Nominal 1 in loses 0.25 in; nominal 8 in loses 0.75 in. |
| 1×10 | 0.75 × 9.25 in | 6.94 sq in | Nominal 1 in loses 0.25 in; nominal 10 in loses 0.75 in. |
| 1×12 | 0.75 × 11.25 in | 8.44 sq in | Nominal 1 in loses 0.25 in; nominal 12 in loses 0.75 in. |
| 2×2 | 1.5 × 1.5 in | 2.25 sq in | Nominal 2 in loses 0.5 in; nominal 2 in loses 0.5 in. |
| 2×3 | 1.5 × 2.5 in | 3.75 sq in | Nominal 2 in loses 0.5 in; nominal 3 in loses 0.5 in. |
| 2×4 | 1.5 × 3.5 in | 5.25 sq in | Nominal 2 in loses 0.5 in; nominal 4 in loses 0.5 in. |
| 2×6 | 1.5 × 5.5 in | 8.25 sq in | Nominal 2 in loses 0.5 in; nominal 6 in loses 0.5 in. |
| 2×8 | 1.5 × 7.25 in | 10.88 sq in | Nominal 2 in loses 0.5 in; nominal 8 in loses 0.75 in. |
| 2×10 | 1.5 × 9.25 in | 13.88 sq in | Nominal 2 in loses 0.5 in; nominal 10 in loses 0.75 in. |
| 2×12 | 1.5 × 11.25 in | 16.88 sq in | Nominal 2 in loses 0.5 in; nominal 12 in loses 0.75 in. |
| 4×4 | 3.5 × 3.5 in | 12.25 sq in | Nominal 4 in loses 0.5 in; nominal 4 in loses 0.5 in. |
| 4×6 | 3.5 × 5.5 in | 19.25 sq in | Nominal 4 in loses 0.5 in; nominal 6 in loses 0.5 in. |
| 6×6 | 5.5 × 5.5 in | 30.25 sq in | Nominal 6 in loses 0.5 in; nominal 6 in loses 0.5 in. |
Setup: a 2×4, 8 feet long — the default stud.
Line 1 — actual size. Thickness 2 is in the 2–6 range, so 2 − 0.5 = 1.5 in. Width 4 is also in range, so 4 − 0.5 = 3.5 in. The board is really 1.5 × 3.5 inches.
Line 2 — board feet. Board feet use the nominal size, not the actual: (2 × 4 × 8) ÷ 12 = 64 ÷ 12 = 5.33 board feet. Board feet are a volume measure for pricing lumber, and the trade prices on nominal volume — so always compute them from the stamped size.
Line 3 — cross-section area. Actual area uses the actual size: 1.5 × 3.5 = 5.25 sq in. This is the number that matters for strength and for fitting: a stud bay framed for a 2×4 holds a 1.5-inch board, not a 2-inch one.
A common floor joist: actual size 1.5 × 9.25 in (the 10-inch width is over 6, so it loses 3/4 inch), board feet 20 — (2 × 10 × 12) ÷ 12 — and cross-section 13.88 sq in. Note how the width rule changes at 6 inches: a 2×6 is 1.5 × 5.5, but a 2×8 jumps to 1.5 × 7.25.
A fence or deck post: actual size 3.5 × 3.5 in, board feet 10.67 — (4 × 4 × 8) ÷ 12 — and cross-section 12.25 sq in. A 4×4 post is not four inches square, which matters when you buy post bases and caps: buy hardware sized for 3.5 inches, not 4.
A shelving or trim board: actual size 0.75 × 5.5 in (the 1-inch thickness finishes at 3/4 inch, the exception to the half-inch rule), board feet 5 — (1 × 6 × 10) ÷ 12 — and cross-section 4.13 sq in. One-inch boards are the trap in this table: if you assumed 0.5 inch thick, your shelf would be a quarter inch thinner than planned on every board.
| Output | Formula | What it means |
|---|---|---|
| Actual thickness / width | 1 in → 0.75; 2–6 in → −0.5; over 6 in → −0.75 | 1.5 × 3.5 in for a 2×4 — the dressed size you actually hold. |
| Board feet | (nominal thickness × nominal width × length in ft) ÷ 12 | 5.33 bf for a 2×4 × 8 ft — the pricing volume, always from nominal size. |
| Cross-section area | actual thickness × actual width | 5.25 sq in for a 2×4 — the real area for strength and fitting. |
| Why the gap exists | drying + planing (surfacing) | Rough lumber is full-size; dressed lumber is planed smooth, losing up to 3/4 inch per dimension. |
Actual sizes are the North American dressed-lumber standard (NIST Voluntary Product Standard PS 20) and hold for surfaced-dry lumber from any major yard; rough-sawn, reclaimed, or imported boards can differ, and a board's thickness can vary slightly with moisture — a wet board measures a hair thicker than a kiln-dried one. Board-foot pricing uses nominal size by trade convention, but some yards price by the piece, so confirm before ordering. Weight note: this page does not compute weight, because it swings wildly with species and moisture — a dry pine 2×4 × 8 ft weighs roughly 9–11 lb, while the same board in wet Douglas fir can weigh 15 lb or more. Always weigh the species and moisture question separately, and check span tables (not this chart) for structural sizing. Error policy: a missing size, a length at or below 0, or a length over 40 ft is reported as an error rather than modeled.
Bright Side Kit. "Lumber Size Chart: Nominal vs Actual Dimensions 2026." https://brightoolbox.com/lumber-size-chart/ Accessed October 24, 2026.Yes, if it is dressed lumber from a North American yard. The 2×4 name is the rough size before drying and planing; surfacing removes half an inch from each dimension in the 2–6 inch range. Rough-sawn boards from a sawmill are the exception — they really are 2 × 4.
Because thin boards start thinner and are surfaced less aggressively. A nominal 1-inch board finishes at 3/4 inch, not 1/2 inch. It is the one exception to the half-inch rule in this table, and it catches a lot of shelf builders by surprise.
Multiply nominal thickness × nominal width × length in feet, then divide by 12. A 2×4 × 8 ft is (2 × 4 × 8) ÷ 12 = 5.33 board feet. Always use nominal size for board feet — the trade prices on nominal volume, even though the board itself is smaller.
1.5 × 9.25 inches. The thickness loses half an inch (2 → 1.5), but the width is over 6 inches, so it loses three-quarters of an inch (10 → 9.25). The same rule gives a 2×12 at 1.5 × 11.25 inches.
3.5 × 3.5 inches. Both dimensions are in the 2–6 range, so each loses half an inch. Buy post bases, caps, and brackets sized for 3.5 inches, not 4.
5.5 × 5.5 inches. Six inches is still in the half-inch-loss range, so a 6×6 post loses half an inch per side. Timbers larger than 6 inches nominal lose three-quarters of an inch instead.
Nominal, always. Board feet are a pricing volume defined on the stamped size. If you computed a 2×4 × 8 ft from actual size you would get 3.5 board feet instead of 5.33 — and every lumber quote you compared would be wrong.
No. This chart is the North American dressed-lumber standard. Rough-sawn boards are full nominal size, and metric or imported boards follow their own standards. If a board measures full-size, it is almost certainly rough-sawn, not mislabeled.