Nominal and Actual Lumber Sizes
When you're shopping for wood for a project, dimensional lumber sizes can get a little confusing. The numbers given for the size of a piece of lumber when you buy it at the store are nominal lumber sizes or measurements. This number indicates the size the wood was originally cut to. Before it’s ready to be sold, dimensional lumber is dried and then planed to make it smooth. Wood shrinks as it dries and the planing or surfacing process removes some of the original material. This means that the wood’s actual measurements are now different from the nominal measurements. If your project requires very specific measurements, it’s important to check what the actual measurements of your lumber are before you purchase it.
Understanding and Identifying Dimensions
The typical nominal dimensions for wood, such as 2 x 4, refer to the thickness and the width of the wood. If a third number is added onto the nominal dimensions, such as 2 x 4 x 96, it indicates the length of the wood.
Hardwood and Softwood Measurements
Different types of wood are sold according to different types of measurements. Softwoods, such as pine, fir, hemlock or spruce have nominal dimensions that include the thickness and the width.
You may see hardwoods, such as hickory, oak, walnut, cherry or birch with nominal dimensions that only include thickness. Hardwoods can also be surfaced on one side only (S1S) or on two sides (S2S), which will further affect the dimensions. Additionally, hardwoods are sold by the volume unit called board foot rather than board dimension. A board foot is calculated by multiplying the nominal thickness, width and length of the cuts of wood.
Common Measurements At-A-Glance
Softwood
Depth x length in inches
- Nominal: 1 x 2 Actual Size: 3/4 x 1-1/2
- Nominal: 1 x 3 Actual Size: 3/4 x 2-1/2
- Nominal: 1 x 4 Actual Size: 3/4 x 3-1/2
- Nominal: 1 x 5 Actual Size: 3/4 x 4-1/2
- Nominal: 1 x 6 Actual Size: 3/4 x 5-1/2
- Nominal: 1 x 8 Actual Size: 3/4 x 7-1/4
- Nominal: 1 x 10 Actual Size: 3/4 x 9-1/4
- Nominal: 1 x 12 Actual Size: 3/4 x 11-1/4
- Nominal: 2 x 2 Actual Size: 1-1/2 x 1-1/2
- Nominal: 2 x 3 Actual Size: 1-1/2 x 2-1/2
- Nominal: 2 x 4 Actual Size: 1-1/2 x 3-1/2
- Nominal: 2 x 6 Actual Size: 1-1/2 x 5-1/2
- Nominal: 2 x 8 Actual Size: 1-1/2 x 7-1/4
- Nominal: 2 x 10 Actual Size: 1-1/2 x 9-1/4
- Nominal: 2 x 12 Actual Size: 1-1/2 x 11-1/4
- Nominal: 4 x 4 Actual Size: 3-1/2 x 3-1/2
- Nominal: 4 x 6 Actual Size: 3-1/2 x 5-1/2
- Nominal: 6 x 6 Actual Size: 5-1/2 x 5-1/2
Hardwood
Thickness in inches
- Nominal: 1/2 S1S: 3/8 S2S: 5/16
- Nominal: 5/8 S1S: 1/2 S2S: 7/16
- Nominal: 3/4 S1S: 5/8 S2S: 9/16
- Nominal: 1 S1S: 7/8 S2S: 13/16
- Nominal: 1-1/4 S1S: 1-1/8 S2S: 1-1/6
- Nominal: 1-1/2 S1S: 1-3/8 S2S: 1 5/16
- Nominal: 2 S1S: 1-13/16 S2S: 1-3/4
- Nominal: 3 S1S: 2-13/16 S2S: 2-3/4
- Nominal: 4 S1S: 3-13/16 S2S: 3-3/4
Conclusion
Are you shopping for a decking or woodworking project? Dimensional lumber sizes can be confusing. Before you head to the store, here are a few tips that should help.
- The lumber that you purchase at the store is sold as a nominal size, which is different than the actual measurement. A nominal size is the original measurement before it's dried. Once it's dried, the wood will shrink so the actual measurements differ. For example, a nominal 2 x 4 measurement has an actual size of 1-1/2 x 3-1/2. This is important to note if you have a project that requires very specific measurements.
- Softwoods (ex. pine, fir, hemlock and spruce) are sold with measurements that include the thickness and the width.
- Hardwoods (ex. hickory, oak, walnut, cherry and birch) are typically sold with a measurement that only includes the thickness.
If you're ready to get started, order your lumber online and have it delivered to your door. Still have questions? Head to your local Lowe's and a Red Vest associate will be happy to help.