The wood species hardness in numbers:
The hardest wood on Janka's scale is Waddywood at 4630 lbs. There are very few on the market since it comes from a protected tree that only grows in 3 places on the Australian continent. It is mostly used for turning, carving and other decorative applications.
Wood in numbers: Balsa is the softest wood with a rating of 70 on the Janka scale. This wood is still considered hardwood since it comes from a hardwood tree.
The Janka hardness test measures the resistance of a wood sample to dents and wear. It measures the force required to embed an 11.28 mm (.444 in.) steel ball into the wood at half the diameter of the ball. This process leaves an imprint. A common use of Janka hardness ratings is to determine if a species is suitable for usessuch as flooring.
The hardness of wood varies with the direction of the grain of the wood. Testing on the surface of a board, perpendicular to the grain, is meant to be for "side hardness". Testing the surface of a cut stump is called an "end hardness" test.
Results are expressed in different ways, which can lead to confusion, especially when the actual units used are not mentionned. In the United States, the measurement is expressed in pound force(lbf). In Sweden, it is in kilogram-force (kgf), and in Australia, either in newtons (N) or kilonewtons (kN). Sometimes the results are taken as units, for example "660 Janka".
The Janka hardness test results in the table below were conducted in accordance with standard ASTM D 1037-12 test methods. The wood stocks tested vary between 1" and 2" thick. The tabulated Janka hardness figures are an average.
The table should not be taken as an absolute; It is intended to help people understand which woods are more resistant to impacts than others.