The Janka scale of hardness starts with Balsa wood (which is technically a hardwood) and has a value of 70 lbf, although there was one sample that achieved a record score of 22lbf. As the values rise, so does the hardness of the wood until we reach the super hard woods like lignum vitae with a rating of 4,390 lbf and finally, the Quebracho (aptly Spanish for axe breaker) species with a top value of 4,570 lbf. As a middle-of-the-road value, White Oak achieves a value of 1,350 lbf. The Janka value refers to the amount of force required to sink a steel ball with a diameter of 0,444 inches halfway into the wood when the moisture content of the wood is twelve percent. You may well wonder why such an odd measurement was selected, and I'm afraid the metric system is to blame for this. The hole made by the 0,444-inch steel ball creates a circle with an area of 100 square millimeters. Check out this video