On the Janka hardness chart, big leaf acacia rates 1700 pounds-force while small leaf acacia rates 2200 pounds-force, and both fall roughly in the middle of the chart. The Janka rating indicates wood strength measured by the force necessary to drive a .444-millimeter steel ball halfway into a plank.
Higher ratings on the Janka hardness chart indicate stronger wood. Among the hardest woods on the Janka chart are Brazilian ebony at 3900 pounds-force and southern chestnut at 3540 pounds-force. Some of the softest woods on the chart include mahogany at 800 pounds-force and California redwood at 420 pounds-force.
Builders commonly use the Janka hardness test to determine how suitable a type of wood is for a particular project. Builders can also use the Janka ratings to anticipate the proper tools necessary to safely work with that type of wood.