Wood Hardness & Density

Some softwoods, like pine, are excellent for construction.

Although trees are broadly grouped into hardwoods and softwoods, it is noteworthy that these categories do not necessarily equate with actual wood hardness. Hardness and density can also vary between sapwood and heartwood on the same tree.

Softwoods and Hardwoods

The terms "softwood" and "hardwood" are not categorized by hardness but rather by a tree's cellular structure. Although not always the case, hardwood trees usually have greater strength than softwoods.

Hardness

Wood hardness is measured by the Janka test, which measures the necessary force to push half of a steel ball's diameter into a sample of wood. The Janka scale is a handy reference for wood flooring specialists and others.

Density

Generally, density correlates with strength and hardness, and super-dense wood, like ironwood, lives up to its name. It is measured by the weight of a given mass of dry wood.

Sapwood and Heartwood

Sapwood is the exterior wood, just below the bark, that still contains some living cells. Heartwood is the interior wood that has no living cells.

Density Charts

Density charts for various tree species are useful woodworking references. For example, low-density wood like balsa (170 kg per cubic meter) is perfect for model building, yet high-density wood like white ash (670 kg per cubic meter) makes durable, beautiful furniture.

References

• "Keeping it All Together: The Preservation and Care of Historic Furniture;" Marc A. Williams; 1990
• TinyTimbers: Janka Hardness Scale
• Conceptualized Reference Database: Density of Wood

Resources

• Read this Article in Spanish