Size, Shapes, and Dimensions of Lumber Unit 6 Size, Shapes, and Dimensions of Lumber Lumber Size • Ordering Lumber • Types of Surfacing • Standard Sizes • Metric Measurement

Nominal thickness and width compared to actual thickness and width. Lumber is usually referred to by its nominal size, which differs from its actual, or dressed, size. See Figure 6‑1. A 2 × 4, for example, is 2″ thick and 4″ wide when it is cut from a log at the sawmill. However, lumber shrinks after being seasoned (air‑dried or kiln‑dried), and surfacing at the planing mill further reduces its measurements. When a 2 × 4 is placed on the market, its actual size is 1 1/2″ × 3 1/2″. Nevertheless, the lumber is referred to as a 2 × 4 (its nominal size) because its original dimensions were 2″ × 4″. See the Appendix for a listing of nominal and actual lumber dimensions.

The abbreviated way of referring to a piece of lumber 2″ thick by 4″ wide by 16′ long is 2 × 4 × 16. Lumber measurements are stated in the following order: thickness, width, and length. For example, a piece of lumber 2″ (nominal size) thick, 4″ (nominal size) wide, and 16′ long is referred to as a 2 × 4 × 16. See Figure 6‑2.

A board foot is equal to a piece of lumber 1″ × 12″ × 12″, or any other measurement that contains 144 cubic inches. Lumber is usually priced by the board foot (BF). A board foot is 1″ thick (nominal size), 12″ wide (nominal size), and 12″ long (1″ × 12″ × 12″), or the equivalent. For example, a piece of lumber 1″ thick, 6″ wide, and 24″ long equals 1 BF. See Figure 6‑3.

Resawn lumber has an attractive textured surface. A special type of rough surfacing is applied to resawn lumber. The pieces are run through a special bandsaw that produces a coarse, textured pattern on the surface of the wood. See Figure 6‑4. Resawn lumber is most often used for exterior trim, siding, or paneling.

The actual size of lumber is always smaller than the nominal size. Boards, Dimension lumber, and Timbers are available in standard sizes. The actual size is always smaller than the nominal size. For example, the actual size of a 2 × 4 is 1 1/2″ thick and 3 1/2″ wide. See Figure 6‑5. Additional standard sizes are found in the Appendix.

A meter is divided into decimeters, centimeters, and millimeters. The meter is the basic unit of linear measurement in the SI metric system. A meter is divided into decimeters (dm), centimeters (cm), and millimeters (mm). See Figure 6-6. Millimeters are the smallest division of a meter used in carpentry and are the standard unit of measurement for materials and metric construction plans.

English and metric measurements may be required to be converted English and metric measurements may be required to be converted. Additional conversions are included in the Appendix. Methods of converting English and metric measurement are shown in Figure 6-7. Conversion tables for area, volume, liquid, weight, pressure, and temperature are found in the Appendix.

Metric lumber and panel sizes are based on the actual sizes and are expressed in millimeters. Metric lumber and panel sizes are based on the actual standard lumber sizes and are expressed in millimeters (mm). See Figure 6-8. For example, the metric lumber size of a 2 × 8, which is 38 × 184, is based on the actual size of 1 1/2″ × 7 1/4″. Actual lumber sizes are converted to their metric equivalents using soft conversion in which little rounding of the equivalents occur. Panel sizes are soft converted or hard converted, depending on the application.