How to Calculate Lumber Sizes

The measuring tape is the primary tool for calculating lumber size.

Calculating the size of lumber means you not only measure the lumber, you also compare the measurements to the standard sizes for lumber to determine whether you have nominal lumber or dimensional lumber. Nominal lumber is lumber which is sized exactly as it's sold: a 2-by-4 is 2 inches thick by 4 inches wide. Dimensional lumber is named for the dimensions it represents: a 2-by-4 is 1 3/4 inches thick by 3 3/4 inches wide. With measurements in hand, you can calculate the size from a standard chart.

Things You'll Need

• Measuring tape
• Chart of standard lumber sizes

Instructions

1. Turn the piece of lumber so that its width is facing upward.

2. Measure the width of the lumber with a tape measure. Hook the tab on the end of the tape on one edge of the lumber and pull the body of the tape measure across the width of the lumber until the body of the tape measure is past the edge of the wood. Read the measurement on the tape at the edge of the lumber you pulled the measuring tape past. Record this measurement.

3. Turn the piece of lumber so that one edge is facing upward.

4. Measure the thickness of the lumber with a tape measure. Hook the tab on the end of the tape on one side of the lumber and pull the body of the tape measure across the thickness of the lumber until the body of the tape measure is past the edge of the wood. Read the measurement on the tape at the edge of the lumber you pulled the measuring tape past. Record this measurement.

5. Look at a chart of nominal and dimensional lumber sizes. If the measurements included fractions, it's dimensional lumber. If not, it's nominal lumber. Find the size lumber that corresponds to the calculated dimensions of the wood you just measured. If it's marked as "dimensional lumber," call it by the name indicated. For example, if the wood was 1 3/4 inches thick and 3 3/4 inches wide, it is dimensional lumber, described as and called by the name of "2-by-4."

Tips & Warnings

• You can obtain paper charts of lumber sizes at any lumber yard and at the website listed in the "references" section below.

References

• Engineer's Edge: Commercial Lumber Sizes

Resources

• Read this Article in Spanish