The Janka (or side) Hardness Test measures the force required to embed a .444 inch steel ball to half it’s diameter in wood. It is one of the best measures of the ability of a wood species to withstand denting and wear. By the same token, it is also a good indicator of how hard or easy a species is to saw or nail.
The Janka hardness test measures the hardness of wood. It measures the force required to embed an 11.28 mm (0.444 in) steel ball into wood to half the ball’s diameter. This method leaves an indentation. It is a good measurement technique to determine the ability of a type of wood withstand denting and wear. It is also a good indicator of how resistant it is to sawing and nailing.
The hardness of wood varies with the direction of the wood grain. Testing on the surface of a plank, perpendicular to the grain, is said to be of “side hardness.” Testing the cut surface of a stump is 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, for example “660 Janka”.
To convert pound-force (lbf) units to newtons N multiply pound-force by 0.45359237 then multiply by 9.80665 (1 standard g in units of m/s2). Janka hardness N = (lbf x 0.45359237) x 9.80665 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.
The Janka Hardness is done in accordance with ASTM D 1037-7 testing methods. Material stocks ranges from 1″ to 2″ thick. (Numbers are an average. Testing is done on samples, not flooring that is already in place.) There is a standard deviation, but these numbers are not published. Other factors affect how flooring performs: type of core (for engineered flooring), grain direction and thickness floor or top wear surface.
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