The hardness (and softness) of wood depends on the context.
Contexts:
(1) type of tree
(2) physical density
Term
Type of Tree
hardwood
angiosperm, usually with broad leaves
softwood
gymnosperm, often an evergreen tree
A hardwood can have a low physical density and a softwood can have a moderate physical density.
Physical density is determined by the Janka hardness test. This involves measuring the force required to push a steel ball measuring 11.29 mm in diameter half-way into the wood. Units are in pounds force, kilogram force, or newtons. The hardness test should be done when the wood has reached a standard moisture content such as 12%.
Tree Species
Typical Janka Hardness in pounds force
Balsa
100
California Redwood or Western White Pine
450
American Cherry or Black Walnut
900
Yellow Birch or Northern Red Oak
1,300
Pecan or Hickory
1,800
Southern Chestnut
3,500
The maximum Janka hardness is around 5,000 lbs force.
The higher the Janka hardness the more durable the material but the harder it is to cut and the heavier its weight.
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