Lumber Sizes: Nominal vs Actual Dimensions Chart
The real dimensions of 1x, 2x, 4x4 and 6x6 lumber in inches and millimeters, the lengths they are sold in, why a 2x4 is not 2 × 4 in, and how to convert to board feet.
A 2x4 actually measures 1 1/2 × 3 1/2 in (38 × 89 mm), and a 2x6 is 1 1/2 × 5 1/2 in (38 × 140 mm). Dimensional lumber is named by its rough-sawn size; drying and planing remove 1/2 in from 2x thicknesses and widths up to 6 in, and 3/4 in from widths of 8 in and more.
- 2x4 actual
- 1 1/2 × 3 1/2 in
- 2x6 actual
- 1 1/2 × 5 1/2 in
- 4x4 actual
- 3 1/2 × 3 1/2 in
- 1x boards
- 3/4 in thick
On this page
Nominal vs actual lumber dimensions chart
Softwood lumber in the US and Canada follows the American Softwood Lumber Standard (PS 20). Sizes below are for dry lumber (19% moisture content or less) surfaced on four sides, which is what home centers sell.
| Nominal size | Actual size (in) | Actual size (mm) | Common uses |
|---|---|---|---|
| 1x2 | 3/4 × 1 1/2 | 19 × 38 | Furring strips, trim backing |
| 1x4 | 3/4 × 3 1/2 | 19 × 89 | Trim, casing, light frames |
| 1x6 | 3/4 × 5 1/2 | 19 × 140 | Fence boards, shelving, baseboard |
| 1x8 | 3/4 × 7 1/4 | 19 × 184 | Shelving, fascia |
| 1x10 | 3/4 × 9 1/4 | 19 × 235 | Shelving, stair risers |
| 1x12 | 3/4 × 11 1/4 | 19 × 286 | Wide shelves, closet shelving |
| 2x2 | 1 1/2 × 1 1/2 | 38 × 38 | Balusters, light framing |
| 2x3 | 1 1/2 × 2 1/2 | 38 × 64 | Non-bearing partitions |
| 2x4 | 1 1/2 × 3 1/2 | 38 × 89 | Wall studs, plates, general framing |
| 2x6 | 1 1/2 × 5 1/2 | 38 × 140 | Exterior walls, decking, rafters |
| 2x8 | 1 1/2 × 7 1/4 | 38 × 184 | Floor joists, rafters, stair stringers |
| 2x10 | 1 1/2 × 9 1/4 | 38 × 235 | Floor and deck joists, headers |
| 2x12 | 1 1/2 × 11 1/4 | 38 × 286 | Long-span joists, stair stringers |
| 4x4 | 3 1/2 × 3 1/2 | 89 × 89 | Fence and deck posts, mailbox posts |
| 4x6 | 3 1/2 × 5 1/2 | 89 × 140 | Beams, heavier posts, landscape steps |
| 6x6 | 5 1/2 × 5 1/2 | 140 × 140 | Deck and pergola posts, retaining walls |
| 8x8 | 7 1/2 × 7 1/2 | 191 × 191 | Timber framing, large posts |
The pattern: thickness and widths up to 6 in lose 1/2 in; widths of 8 in and over lose 3/4 in; 1x boards are 3/4 in thick. Timbers 5 in and thicker (6x6, 8x8) are usually surfaced green and lose 1/2 in in each direction.
Why a 2x4 is not 2 by 4 inches
A 2x4 starts as a rough-sawn board close to 2 × 4 in. It then shrinks as it dries and is planed smooth on all four sides, which removes about 1/4 in from each face. The name stayed with the rough size.
- Green vs dry sizes: PS 20 sets slightly larger minimum sizes for lumber surfaced while green (over 19% moisture) so that it ends up close to dry sizes after shrinking. A green 2x4 is 1 9/16 × 3 9/16 in; a green 2x10 is 1 9/16 × 9 1/2 in.
- Pressure-treated lumber is usually dried before treatment and then soaked again, so it is often a little oversize and heavy when new. Expect it to shrink by up to about 1/16 in in thickness, and leave small gaps between deck boards accordingly.
- Older houses: lumber in homes built before the 1960s is often fuller, close to 1 5/8 × 3 5/8 in, or even a true 2 × 4 in rough-sawn. Repairs may need shims or ripped boards to line up.
Standard lumber lengths
| Length | Inches | Meters | Notes |
|---|---|---|---|
| Precut stud (8 ft wall) | 92 5/8 | 2.353 | With three plates, gives a 97 1/8 in wall: room for 8 ft drywall plus a ceiling layer |
| Precut stud (9 ft wall) | 104 5/8 | 2.657 | Same logic, 9 ft ceilings |
| Precut stud (10 ft wall) | 116 5/8 | 2.962 | 10 ft ceilings |
| 8 ft | 96 | 2.438 | The most common length for 2x4s and 1x boards |
| 10 ft | 120 | 3.048 | Rafters, joists, top plates |
| 12 ft | 144 | 3.658 | Joists and deck boards |
| 16 ft | 192 | 4.877 | Deck boards, rim joists, long plates |
| 20 ft | 240 | 6.096 | Longest common stock; longer spans use engineered lumber |
Lengths come in 2 ft steps. Plan cuts so that offcuts are useful: a 12 ft 2x4 gives three 4 ft blocks, and a 16 ft deck board spans exactly 12 joist bays at 16 in on center.
Lumber sizes in mm (metric countries)
Canada uses the same dimensions as the US and sells them in imperial names. Elsewhere, timber is sold by its actual metric size.
| Region | Common sizes (mm) | Closest US size |
|---|---|---|
| UK, CLS (planed) | 38 × 63, 38 × 89, 38 × 140 | 2x3, 2x4, 2x6 |
| UK, regularised C16/C24 | 47 × 75, 100, 150, 200, 225 | Thicker than any 2x (1.85 in) |
| Australia, MGP10 | 70 × 35, 70 × 45, 90 × 35, 90 × 45 | 90 × 45 is close to a 2x4 in width but 7 mm thicker |
| Continental Europe | Varies by country, often 45 × 95 to 45 × 220 | no direct match |
UK lengths step by 300 mm, from 2.4 m to 4.8 m and longer. A UK 2.4 m length is 38 mm (1 1/2 in) shorter than a US 8 ft board.
Plywood and OSB sheet sizes
Sheet goods are 4 × 8 ft (48 × 96 in, 1,219 × 2,438 mm), with 4 × 9 and 4 × 10 ft sheets for tall walls. Their thickness is also nominal: most structural panels are sold under an "actual" thickness 1/32 in thinner than their name.
| Nominal | Actual (in) | Actual (mm) | Typical use |
|---|---|---|---|
| 1/4 in | 7/32 (often sold as 1/4) | 5.6 | Cabinet backs, drawer bottoms |
| 3/8 in | 11/32 | 8.7 | Underlayment, crafts |
| 1/2 in | 15/32 | 11.9 | Wall and roof sheathing |
| 5/8 in | 19/32 | 15.1 | Roof sheathing at 24 in spacing |
| 3/4 in | 23/32 | 18.3 | Subfloors, cabinets, shelving |
Metric sheets are 1,220 × 2,440 mm or 1,250 × 2,500 mm in 9, 12, 15 and 18 mm thicknesses. A 2,440 mm sheet is 2 mm longer than a US sheet, which matters only for tight cabinet work.
Hardwood thickness (the quarter system)
Hardwood is sold rough in quarters of an inch and by the board foot, with random widths and lengths. Surfaced on two sides (S2S), it ends up thinner.
| Quarter size | Rough thickness | Surfaced (S2S) |
|---|---|---|
| 4/4 | 1 in (25 mm) | 13/16 in (21 mm) |
| 5/4 | 1 1/4 in (32 mm) | 1 1/16 in (27 mm) |
| 6/4 | 1 1/2 in (38 mm) | 1 5/16 in (33 mm) |
| 8/4 | 2 in (51 mm) | 1 3/4 in (44 mm) |
| 12/4 | 3 in (76 mm) | 2 3/4 in (70 mm) |
Softwood "5/4" deck boards are a different product: a 5/4 × 6 radius-edge deck board is 1 × 5 1/2 in (25 × 140 mm).
Board feet: how lumber volume is measured
A board foot is 144 cubic inches, a piece 1 in thick, 12 in wide and 12 in long. It is calculated from nominal sizes: thickness (in) × width (in) × length (ft) ÷ 12.
| Piece | Calculation | Board feet |
|---|---|---|
| 1x6, 8 ft | 1 × 6 × 8 ÷ 12 | 4 |
| 2x4, 8 ft | 2 × 4 × 8 ÷ 12 | 5.33 |
| 2x6, 8 ft | 2 × 6 × 8 ÷ 12 | 8 |
| 2x10, 12 ft | 2 × 10 × 12 ÷ 12 | 20 |
| 4x4, 8 ft | 4 × 4 × 8 ÷ 12 | 10.67 |
| 6x6, 10 ft | 6 × 6 × 10 ÷ 12 | 30 |
Because the formula uses nominal sizes, you pay for wood that was planed away: a 2x4's actual cross-section is 5.25 sq in, about 66% of the nominal 8 sq in.
How much a 2x4 weighs
An 8 ft 2x4 holds 0.29 cu ft of wood. At typical dry densities, that is about 7.5 to 8.5 lb (3.4 to 3.9 kg) for spruce-pine-fir and 10 to 11 lb (4.5 to 5 kg) for southern yellow pine. Freshly pressure-treated pine can weigh 50% more until it dries. These are calculated from the piece's volume and species density, so a wet or knotty board will differ.
Always design with actual dimensions. Three 2x6 deck boards with 1/8 in gaps cover 16 3/4 in, not 18 in. A wall of 2x4 studs with 1/2 in drywall on both sides is 4 1/2 in thick, which is why interior door jambs are 4 9/16 in wide.
For fastening, see nail sizes and screw sizes. For outdoor builds, the deck dimensions guide covers joist and board layouts, and shed sizes shows footprints that waste the least lumber. Reclaimed wood from pallets is usually thinner than 1x lumber.
Frequently asked questions
What is the actual size of a 2x6?
1 1/2 × 5 1/2 in (38 × 140 mm) when dry. Freshly pressure-treated or green 2x6s can measure up to about 1 9/16 × 5 5/8 in and shrink as they dry.
What is a 2x4x8 in mm?
38 × 89 × 2,438 mm. The 8 ft length is real, while the 2 × 4 in cross-section is nominal. A precut stud for an 8 ft wall is shorter, at 92 5/8 in (2,353 mm).
What lengths do 2x4s come in?
Even-foot lengths from 8 to 20 ft are standard (8, 10, 12, 14, 16, 18 and 20 ft), plus precut studs of 92 5/8 in, 104 5/8 in and 116 5/8 in for 8, 9 and 10 ft walls. Some stores also stock 6 ft and 24 ft pieces.
Are 8 foot boards actually 8 feet long?
Yes. Unlike width and thickness, lumber length is not reduced: an 8 ft board is at least 96 in and often a fraction of an inch longer, which leaves room to square the ends. Precut studs are the exception.
What are the standard lengths of 4x4 lumber?
4x4 posts (3 1/2 × 3 1/2 in) are commonly sold in 8, 10, 12 and 16 ft lengths, with 6 ft pieces for fence and mailbox posts. Pressure-treated ground-contact posts are the usual choice for anything set in soil or concrete.
Can I use 4x4 posts instead of 6x6 for a treehouse or deck?
A 6x6 (5 1/2 in square, 30.25 sq in) has about 2.5 times the cross-section of a 4x4 (12.25 sq in) and resists buckling far better on tall posts. The 2018 IRC limits 4x4 deck posts to 6 ft 9 in to 8 ft depending on the beam and allows 6x6 posts to 14 ft; the 2021 table also varies with species, snow load and deck area. See our tree house guide and confirm with your building department.