Dimensional Lumber Size Reference
A complete guide to nominal vs. actual dimensions for standard framing lumber, boards, and structural timbers.
Get a Free Quote
Tell us about your project and we'll respond within 24 hours.
Understanding Lumber Sizes
Lumber is sold by its nominal size, which is the rough-cut dimension before drying and planing. The actual size is what you get at the lumber yard. For example, a “2×4” actually measures 1-1/2″ × 3-1/2″. This difference matters when planning framing layouts, calculating material requirements, and ensuring proper fit.
Note for reclaimed lumber: Older reclaimed lumber was often cut to true nominal dimensions. A reclaimed 2×4 may actually measure a full 2″ × 4″, which can affect compatibility with modern framing. Always verify dimensions before mixing reclaimed and new lumber in the same project.
Framing Lumber (2× Series)
The 2× series is the backbone of residential and light commercial construction. Used for wall studs, floor joists, roof rafters, and headers.
| Nominal Size | Actual Size (in) | Actual Size (mm) | Common Uses |
|---|---|---|---|
| 2 × 2 | 1-1/2 × 1-1/2 | 38 × 38 | Furring strips, light framing, craft |
| 2 × 3 | 1-1/2 × 2-1/2 | 38 × 64 | Furring, utility framing |
| 2 × 4 | 1-1/2 × 3-1/2 | 38 × 89 | Wall studs, plates, light framing |
| 2 × 6 | 1-1/2 × 5-1/2 | 38 × 140 | Exterior walls, floor joists, rafters |
| 2 × 8 | 1-1/2 × 7-1/4 | 38 × 184 | Floor joists, rafters, headers |
| 2 × 10 | 1-1/2 × 9-1/4 | 38 × 235 | Floor joists, beams, stair stringers |
| 2 × 12 | 1-1/2 × 11-1/4 | 38 × 286 | Ridge boards, long-span joists, headers |
Boards (1× Series)
One-by boards are used for trim, shelving, siding, sheathing, and finish carpentry.
| Nominal Size | Actual Size (in) | Actual Size (mm) | Common Uses |
|---|---|---|---|
| 1 × 2 | 3/4 × 1-1/2 | 19 × 38 | Furring, lattice, small trim |
| 1 × 3 | 3/4 × 2-1/2 | 19 × 64 | Trim, battens |
| 1 × 4 | 3/4 × 3-1/2 | 19 × 89 | Trim, siding, craft projects |
| 1 × 6 | 3/4 × 5-1/2 | 19 × 140 | Fencing, shelving, paneling |
| 1 × 8 | 3/4 × 7-1/4 | 19 × 184 | Shelving, siding, sheathing |
| 1 × 10 | 3/4 × 9-1/4 | 19 × 235 | Wide shelving, cabinet sides |
| 1 × 12 | 3/4 × 11-1/4 | 19 × 286 | Shelving, stair treads, wide trim |
Structural Timbers (4×4 and Larger)
Timbers 4×4 and larger lose 1/2″ per dimension during finishing. For 5×5 and above (often called “timbers” rather than “lumber”), the actual size is typically 1/2″ less than nominal on each dimension.
| Nominal Size | Actual Size (in) | Common Uses |
|---|---|---|
| 4 × 4 | 3-1/2 × 3-1/2 | Posts, deck supports, railing |
| 4 × 6 | 3-1/2 × 5-1/2 | Headers, beams, columns |
| 6 × 6 | 5-1/2 × 5-1/2 | Heavy posts, columns, pergolas |
| 6 × 8 | 5-1/2 × 7-1/2 | Beams, girders |
| 8 × 8 | 7-1/2 × 7-1/2 | Structural beams, timber framing |
Standard Lengths
Dimensional lumber is stocked in even-foot increments. The most common lengths at retail are:
Reclaimed lumber lengths vary depending on the source structure. We carry pieces ranging from 4 feet to 40+ feet. Longer lengths are available in beams and timbers.
Stud Lengths and Wall Heights
Studs are sold in pre-cut lengths corresponding to standard wall heights. The most common lengths account for top and bottom plates while delivering finished interior heights of 8, 9, or 10 feet.
| Stud Length | Wall Plate Configuration | Finished Wall Height | Common Use |
|---|---|---|---|
| 92-5/8″ (PET) | 1 bottom + 2 top plates | ~8′ 1″ | Standard 8 ft residential walls |
| 104-5/8″ | 1 bottom + 2 top plates | ~9′ 1″ | 9 ft ceiling residential |
| 116-5/8″ | 1 bottom + 2 top plates | ~10′ 1″ | 10 ft ceiling residential |
| 92-1/4″ | Standard plates | 8′ exact | Where strict 8 ft height required |
| 96″ (8 ft) | Custom cut to length | Variable | Garages, sheds, accessory structures |
The 92-5/8 inch stud: The pre-cut PET (precision end-trimmed) stud is cut to 92-5/8 inches so that adding a single bottom plate (1-1/2″) and a double top plate (3″) yields exactly 96-1/8″ — leaving room for a half-inch ceiling drywall and a finished 8 ft interior height with 1/2″ clearance.
Floor Joist Span Reference
Allowable span varies by species, grade, spacing, and live load. The values below are typical maximums for No. 2 grade Douglas Fir-Larch supporting a 40 psf live load and 10 psf dead load (residential floors). Always confirm spans with local code and an engineer when in doubt.
| Joist Size | 12″ o.c. | 16″ o.c. | 19.2″ o.c. | 24″ o.c. |
|---|---|---|---|---|
| 2 × 6 | 10′ 9″ | 9′ 9″ | 9′ 2″ | 8′ 6″ |
| 2 × 8 | 14′ 2″ | 12′ 10″ | 12′ 1″ | 11′ 0″ |
| 2 × 10 | 18′ 0″ | 16′ 1″ | 15′ 2″ | 13′ 5″ |
| 2 × 12 | 21′ 4″ | 18′ 7″ | 17′ 7″ | 15′ 7″ |
Rafter Span Reference
Roof rafter spans depend on snow load, dead load, slope, and species. The following are representative maximum horizontal spans for No. 2 Douglas Fir-Larch under 30 psf snow load.
| Rafter Size | 12″ o.c. | 16″ o.c. | 24″ o.c. |
|---|---|---|---|
| 2 × 4 | 8′ 7″ | 7′ 9″ | 6′ 9″ |
| 2 × 6 | 13′ 6″ | 12′ 3″ | 10′ 9″ |
| 2 × 8 | 17′ 9″ | 16′ 1″ | 14′ 1″ |
| 2 × 10 | 22′ 8″ | 20′ 6″ | 17′ 11″ |
| 2 × 12 | 27′ 7″ | 25′ 0″ | 21′ 10″ |
Header Sizing Guide
Headers carry the load above door and window openings. Properly sized headers prevent sagging and ensure long-term structural integrity. The values below assume a residential wall supporting a roof and one floor above.
| Opening Width | Header Size (Doug Fir) | Trimmer Studs Required |
|---|---|---|
| Up to 3′ 0″ | 2 × 4 (single) | 1 each side |
| 3′ 1″ to 5′ 0″ | (2) 2 × 6 | 1 each side |
| 5′ 1″ to 6′ 6″ | (2) 2 × 8 | 1 each side |
| 6′ 7″ to 8′ 0″ | (2) 2 × 10 | 2 each side |
| 8′ 1″ to 10′ 0″ | (2) 2 × 12 | 2 each side |
| 10′ 1″ to 12′ 0″ | (3) 2 × 12 or LVL | 3 each side |
| Over 12′ | Engineered LVL or steel | Per engineer |
Built-up headers: Two pieces of dimensional lumber are sandwiched with a 1/2″ plywood spacer to create a 3-1/2″ thick header that aligns with a 2x4 wall. For 2x6 walls, use 1″ foam or two layers of 1/2″ plywood between the header members.
Moisture Content Designations
Lumber moisture content affects size, weight, strength, and stability. Grade stamps include a moisture designation that tells you how the lumber was processed before grading.
S-GRN (Surfaced Green)
Lumber surfaced while moisture content exceeds 19%. Will shrink as it dries. Sold slightly oversize to compensate. Common in heavy timbers and large dimension stock.
S-DRY (Surfaced Dry)
Surfaced when moisture content is 19% or less. Standard for most framing lumber. Stable enough for construction without significant additional shrinkage.
KD-HT (Kiln Dried, Heat Treated)
Kiln dried to 19% or less and heat-treated to kill insects and pathogens. Required for international shipping under ISPM-15 regulations. Typical for premium framing.
KD15 / MC15
Kiln dried to 15% maximum moisture content. Higher quality stock for finish work, trim, and millwork where dimensional stability is critical.
EMC (Equilibrium Moisture)
The moisture level wood will reach in a given environment. Indoor conditioned spaces in California typically reach 8 to 10% EMC. Acclimate lumber before installation.
Reclaimed (Air Dry)
Most reclaimed lumber has long since reached equilibrium with its environment, often at 8 to 12% MC. This is one of the key stability advantages of well-aged reclaimed stock.
Lumber Shrinkage by Species
Wood shrinks as it dries from green to oven dry. Tangential shrinkage (across the rings) is always greater than radial shrinkage (across the rays), which is why flatsawn boards cup and quartersawn stock stays flat.
| Species | Tangential Shrinkage | Radial Shrinkage | Volumetric |
|---|---|---|---|
| Douglas Fir | 7.6% | 4.8% | 12.4% |
| Coast Redwood | 4.4% | 2.6% | 6.8% |
| Western Red Cedar | 5.0% | 2.4% | 6.8% |
| White Oak | 10.5% | 5.6% | 16.3% |
| Red Oak | 8.6% | 4.0% | 13.7% |
| Hard Maple | 9.9% | 4.8% | 14.7% |
| Ponderosa Pine | 6.2% | 3.9% | 9.7% |
| Black Walnut | 7.8% | 5.5% | 12.8% |