Janka Wood Hardness Test - USDA Public Information Page - CIF434

The Janka Hardness Test Measures The Hardness Of Wood. It involves measuring the force required to embed a 11.28 millimeter (0.444 inch) steel ball into wood to half its diameter. This method was chosen so that the result would leave an indention 100 square millimeters in size. 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, perpendicular to the grain, the test is said to be of "side hardness." Testing the cut surface of a stump would be called a test of "end hardness."

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".

To convert the United States pound-force (lbf) units to newtons N multiply pound-force by 0.453 592 37 then multiply by 9.8. Janka hardness N = (lbf x 0.453 592 37)9.8 OR multiply by 4.44822161526. To get lbf from N, multiply N by 0.224808943099736.

A common use of Janka hardness ratings is to determine whether a species is suitable for use as flooring.

Wood Flooring Species ------------- Janka Hardness (pounds-force)

Lignum Vitae 4500

Brazilian Ebony 3692

Ipe / "Brazilian Walnut" / Lapacho 3684

African Pearlwood / Moabi 3680