Janka Hardness Scale

Wood Density Information

Janka Hardness: A measure of the hardness of wood, produced by a variation on the Brinell hardness test. The test measures the force required to push a steel ball with a diameter of 11.28 millimeters (0.444 inches) into the wood to a depth of half the ball’s diameter (the diameter was chosen to produce a circle with an area of 100 square millimeters). In Janka's original test, the results were expressed in units of pressure, but when the ASTM standardized the test (tentative issue in 1922, standard first formally adopted in 1927), it called for results in units of force.

The results are stated in various ways in different countries, which can lead to confusion, especially since the name of the actual unit employed is often not attached. In the United States, the measurement is in pounds-force. In Sweden it is apparently in kilogram-force (kgf), and in Australia, Janka hardness ratings are either in newtons (N) or kilonewtons (kN). Sometimes the results are treated as units, e.g., “360 janka.”

The hardness of wood usually varies with the direction of the grain. If testing is done on the surface of a plank, with the force exerted perpendicular to the grain, the test is said to be of “side hardness.” Side hardness of a block of wood measured in the direction of the tree's center (radially), and on a tangent to the tree's rings (tangentially), are typically very similar. End testing is also sometimes done (that is, testing the cut surface of a stump would be a test of end hardness). The side hardness of teak, for example, is in the range 3730 to 4800 newtons, while the end hardness is in the range 4150 to 4500 newtons.

  • Ipe 3680 (approx. 3 times harder than Oak).
  • Cumaru 3540
  • Massaranduba 3190
  • Angelim Pedra 3040
  • Tigerwood 2620
  • Jatoba 2350
  • Garapa 2280
  • Batu 2100
  • Purple Heart 1860
  • Red Oak 1290
  • Keruing 1270 (truck decking).
  • Teak 1155
  • Honduran Mahogany 900
  • Mahogany 800
  • Dark Red Meranti 780
  • Southern Yellow Pine 680
  • Douglas Fir 660
  • Spanish Cedar 600
  • Alaskan Yellow Cedar 580
  • Cypress 460
  • Western Red Cedar 350