Name Hickory
Location Eastern North America
Texture/Grain Medium/Open
Specific Gravity 0.82
Hardness Very Hard
Strength Very Strong
T/R Stability 10.2/7.0%

GRAIN DIRECTION AND STRENGTH
To take full advantage of a wood’s strength, pay attention to the grain direction. Wood is a natural polymer — parallel strands of cellulose fibers held together by a lignin binder. These long chains of fibers make the wood exceptionally strong — they resist stress and spread the load over the length of the board. Furthermore, cellulose is tougher than lignin. It’s easier to split a board with the grain (separating the lignin) than it is to break it across the grain (separating the cellulose fibers). 

Remember this when you lay out the parts of a project. Always orient the grain so the fibers support the load. Whenever possible, cut the parts so the grain is continuous, running the length of the board. This also applies to wood joinery! When cutting a tenon, for example, the wood grain must run the length of the tenon and the board so the grain is continuous.

A "three-point" test to measure bending strength.

SPECIFIC GRAVITY
When strength is paramount, grain direction may not be your only consideration. Some species of wood are naturally stronger than others. Chairmakers, for example, typically use maple, birch, and hickory for legs, rungs, and spindles. These parts are fairly slender, and weaker woods won’t hold up.

A good indicator of a wood’s strength is its density — the weight for a given volume. This is measured by its specific gravity — the weight of a volume of wood divided by the weight of the same volume of water. Generally, the higher the ratio, the denser and stronger the wood. This is not always the case, but specific gravity is a useful reference nonetheless.

ADDITIONAL MEASUREMENTS OF STRENGTH
In some woodworking situations, “strength” is an ambiguous term. To say oak is strong doesn’t tell you whether an oak shelf will sag when loaded with heavy objects, or whether its surface is hard enough to resist scratches and dents. You may need better information. Engineers have devised ways to measure specific types of strength.

• Compressive strength tells you how much of a load a wood species can withstand parallel to the grain. How much weight will the legs of a table support before they buckle?
• Bending strength (also known as the modulus of rupture) shows the load the wood can withstand perpendicular to the grain. How much weight can you hang on a peg?
• The stiffness or modulus of elasticity indicates how much the wood will deflect when a load is applied perpendicular to the grain. How far will those shelves sag?
• The hardness reveals how resistant the surface of the wood is to scratches, dents, and other abuse. How long will that kitchen counter stay looking new and unmarred?

To compare the strengths and specific gravities of common domestic and imported woods, refer to the charts below in  “Relative Wood Strengths.”
 

Wood has several kinds of strength. For a rough, general estimate of strength, refer to the specific gravity or density of the wood. When you need more detailed information, there are additional choices.

Engineers measure the compressive strength by loading a block of wood parallel to the grain until it breaks, and the bending strength by loading a block perpendicular to the grain. Both are measured in pounds per square inch (psi). Stiffness is determined by applying a load to a beam until it deflects a certain amount, and it’s measured in millions of pounds per square inch (Mpsi). To find hardness, engineers drive a metal ball halfway into the wood’s surface. The force used is recorded in pounds (lb). In each case, the higher the number, the stronger the wood.

NORTH AMERICAN HARDWOODS

NORTH AMERICAN SOFTWOODS

WORLD WOODS (OTHER THAN NORTH AMERICA)

*After kiln-drying. Specific gravity may be slightly higher in green wood.
†Rating not available — species has not been tested.
 

Back to the top

*Indicates that you can enlarge a photo by clicking on it. To reveal the information in a "Superphoto," first enlarge it and then move the cursor over it.