Lumber Dimensions Reference Chart
Photo via Unsplash
Complete guide to nominal vs actual lumber sizes, plywood thicknesses, and hardwood specifications
Photo via Unsplash
Complete guide to nominal vs actual lumber sizes, plywood thicknesses, and hardwood specifications
Dimensional lumber is sold by its nominal size, which differs from its actual dimensions after drying and planing. The table below shows the most common sizes used in construction and woodworking.
| Nominal Size | Actual (inches) | Actual (mm) | Board Feet per Linear Foot |
|---|
| Nominal Size | Actual (inches) | Actual (mm) | Board Feet per Linear Foot |
|---|
| Nominal Size | Actual (inches) | Actual (mm) | Board Feet per Linear Foot |
|---|
Dimensional lumber is typically available in the following standard lengths:
Lengths over 16 feet may need to be special ordered. Lumber yards often stock longer lengths than big-box stores. For structural applications requiring long spans, consider engineered lumber products like LVL beams.
Like dimensional lumber, plywood is sold by nominal thickness but the actual measurement is slightly less. This is important for dado joints and shelf supports.
| Nominal Thickness | Actual (inches) | Actual (mm) | Common Uses |
|---|
When cutting dadoes for plywood shelves, always measure your actual plywood thickness first. Using a 3/4" dado bit for 3/4" plywood will result in a loose fit since the plywood is actually 23/32".
Hardwood lumber is sold in quarter increments, measured in quarters of an inch. The rough thickness is the nominal size; surfaced lumber (S2S) will be thinner.
| Quarter Size | Rough Thickness | Surfaced (S2S) | Common Name |
|---|
When planning projects, account for material loss during surfacing. If you need 3/4" finished thickness, buy 4/4 rough lumber. For 1-1/2" finished, buy 8/4 rough. Always add 15-20% extra for waste, defects, and mistakes.
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Lumber dimensions are given in nominal sizes, which represent the rough-cut size before drying and planing. When lumber is first cut from a log, it is close to the nominal dimensions. However, during the drying process (either air-dried or kiln-dried) the wood shrinks. Then it goes through a planer to create smooth, consistent surfaces, removing additional material. This process typically removes about 1/2 inch from each dimension, resulting in the smaller actual size you purchase. The nominal naming convention has been standardized since 1964.
A nominal 2x4 has actual dimensions of 1.5 inches by 3.5 inches (38mm x 89mm). This applies to kiln-dried dimensional lumber commonly sold at lumber yards and home improvement stores. Green (wet) lumber may be slightly larger as it hasn't fully dried yet. When calculating materials for construction projects, always use the actual dimensions for accurate measurements.
Hardwood lumber thickness is measured in quarters of an inch, expressed as a fraction over 4. So 4/4 (pronounced "four-quarter") means 4/4 of an inch, or 1 inch rough thickness. Common sizes include: 4/4 = 1", 5/4 = 1-1/4", 6/4 = 1-1/2", 8/4 = 2", 10/4 = 2-1/2", 12/4 = 3", and 16/4 = 4". After surfacing (S2S - surfaced two sides), expect to lose about 3/16" from each face, so 4/4 lumber becomes approximately 13/16" thick when surfaced.
Standard dimensional lumber (2x4, 2x6, etc.) comes in lengths from 8 feet to 20 feet, typically in 2-foot increments. The most common lengths stocked at retail stores are 8, 10, 12, 14, and 16 feet. Longer lengths (18-20 feet) may need to be special ordered or purchased from a lumber yard. Hardwood lumber is typically sold in random lengths, usually ranging from 4 to 16 feet, and is priced by the board foot rather than by the piece.