Janka Hardness Ratings for Wood Siding
The industry standard method for determining the hardness of wood products is called the Janka hardness test.
Janka hardness of a given wood species is defined by a resistance to indentation test as measured by the load
(pounds of pressure) required to embed a
11.28mm or 0.444" diameter ball to one-half its diameter into the wood. The Janka values presented are the
average of penetrations on both flat grain or plain sawn and vertical grain or quartersawn boards.
The Wood Handbook - Wood as an Engineering Material, USDA, General Technical Report 113.