Janka Hardness Test

The Janka test measures the force required to embed a 11.28 millimeter (0.444 inch) steel ball into wood to half its diameter.
It is one of the best measures of the ability of a wood species to withstand denting and wear. It is also a good indicator of how hard a species is to saw or nail.
The hardness of wood usually varies with the direction of the wood grain. If testing is done on the surface of a plank, the test is said to be of "side hardness." Testing the cut surface of a stump would be called a test of "end hardness."
The results are stated in various ways, which can lead to confusion, especially when the name of the actual units employed is often not attached. In the United States, the measurement is in pounds-force (lbf). In Sweden it is in kilograms-force (kgf), and in Australia, either in newtons (N) or kilonewtons (kN). Sometimes the results are treated as units, e.g., "660 Janka."

Douglas Fir, a relatively soft wood, has a Janka hardness rating of 660 lbf. Brazilian cherry, a very hard wood, has a rating of 2350 lbf, while Brazilian Walnut has a hardness rating of 3800 lbf.
A common use of Janka hardness ratings is to determine whether a species is suitable for use as flooring.

Wood Floor Hardness Rating
Wood Species	Rating Unit*
Douglas Fir	660
S. Yellow Pine, Shortleaf	690
S. Yellow Pine, Longleaf	890
Black Cherry	950
Teak	1000
Black Walnut	1010
Heartpine	1225
Yellow Birch	1260
Oak, Red Northern	1290
Beech, American	1300
Ash, White	1320
Oak, White	1360
Cypress, Australian	1375
Hard Maple	1450
Wenge	1620
Bamboo, Timbergrass	1642
African Pedauk	1725
Hickory	1820
Pecan	1820
Purpleheart	1860
Jarrah	1910
Merbau	1925
Santos Mahogany	2200
Mesquite	2345
Brazilian Cherry	2350
Brazilian Walnut	3800
*A higher number means harder wood; lower number, softer wood.