To fully understand the Janka Hardness Scale, perhaps it is best to first explore what is called the Janka Hardness Test. It is a process that uses applied pressure to embed a 11.28 millimeter (or 0.444 inch) steel ball into the face, side, or end of a piece of wood. The amount of pressure exerted – usually measured in PSI (Pounds/square inch) – relates effectively to the quotient of the Janka rating. For example, Santos Mahogany bears a rating of 2200 on the Janka Scale, equating to 2200 PSI to press the steel ball into the wood up to half of its diameter.
The placement of the steel ball can affect the classification of the rating. A face test of the desired wood is the usual rating. The two other types are end and side quotients. An end quotient refers to the end of a plank of wood, as implied with the title. A side rating, similarly, is the rating taking on the side of the wood. The main difference between these three is in relation to the cut of the wood, and patterns of the grain. At the end of a plank of wood, a steel ball will more easily slip into the wood because of the configuration of the grain at the end of the plank. A side rating will be closer to the face rating, but the face rating is the most accurate since the face of a plank is what is exposed to the traffic.
The Janka rating list of hardwood species ranges from about 380 (Eastern White Pine) to around 3680 (Ipe, also known as Brazilian Walnut), giving a wide range of varying hardness. Dozens of species lie in between the top and bottom contenders. Red Oak is often considered the middle point, with a rating of 1280. Brazilian Cherry, one of the more popular floorings in recent years, ranks higher at 2350.
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