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Understanding Nominal and Actual Lumber Sizes

Lowe's Editorial Team

By Lowe's Editorial Team
Published July 22, 2022

If you’ve ever bought a cut of wood from the store and measured it at home, you might have noticed that the lumber’s actual size isn’t the same as the size it’s marketed as. In this guide, we discuss why this happens and what some common measurements are.

A wood deck with patio furniture and a deck box next to a yellow house.

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