International Janka Hardness

Model: Janka Hardness | Date:2010-05-13

 
 
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 units 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 hardnesses 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. 
 
The most common use of Janka hardness ratings is to determine whether a species is suitable for use as flooring.
 

 

English name

Latin name

side hardness/ Janka test

at 12% moisture content

kilonewtons

pounds-force

courbaril, jatoba

Hymenaea courbaril l.

10.8

2550

sucupira

Diplotropis purpurea

9.5

2140

Balsamo

Myroxylon spp.

8.7

2200

merbau

Intsia spp.

8.2

1925

Tigerwood

Astronium gracile

7.9

1850

Doussie

Afzelia africana spp.

7.7

1770

kempas

Koompassia malaccensis

7.6

1710

afromosia

Pericopsis elata

7.1

1560

sapele

Entandrophragma cylindricum sprague

6.7

1510

Hard maple

Acer spp.

6.6

1450

white oak

Quercus spp.

6

1360

beech

Fagus spp.

5.8

1300

red oak

Quercus rubra

5.7

1290

iroko

Chlorophora spp.

5.6

1260

burma teak

Tectona spp.

4.6

1150

black walnut

Juglans nigra l.

4.5

1010

American cherry

Prunus serotina ehrh

4.2

950

birch

Betula spp.

3.4

760