The hardness of wood is measured with the Janka Hardness test. The Janka Hardness test measures the force needed to embed a .444 inch steel ball to half its diameter in a piece of wood. The higher the number the harder the wood.  Although this is one of the best methods to measure the ability of wood species to withstand indentations, it should be used only as a general guide when comparing various species of wood flooring. The construction and finish also play an important role in the durability of any wood floor.