In the flooring world, the Janka scale is used to rate woods for hardness. According to the Janka scale, the hardest woods used for flooring are Patagonia Rosewood (3840), Brazilian Walnut (3680), and Brazilian Ebony (3585). Are you ready for a great twist? Bamboo, which is technically a grass, tops them all with a 5,000 hardness rating. The Douglas fir comes in at 660 on the Janka scale, the lowest and softest wood. There are other woods, and some exceed the 5000 Janka rating, but they are not used in the United States for flooring. Hard does not always translate to durable or practical.