Hardness rating: the hardness rating of a timber species is measured by the Janka Test. This is a standard test which measures the penetration into the timber of a common load and projectile. The results relate to a hardness capacity of the material and are expressed in kN. This information is useful where the timber may be subject to potential damage from impacts e.g. a dance floor. There are 2 sets of published figures; one for 'Green' or freshly felled timber and one for seasoned timber - i.e. timber with a moisture content of 12%.
The ratings given here are:
Soft - less than 5.5
Moderate - 5.5 to 7.0
Hard - 7.1 to 10.0
Very Hard - greater than 10.0.
The Janka test in reality means nothing.
It use to be a set weight & size ball bearing dropped from a set height when I did my TAFE block training about 15 years ago.
You drop something from height on Hevea & then do the same to Ironwood which is at the other end of the Janka scale & they are both dented, scratched, damaged.
To me in practical experience it means nothing.
My opinion only, but if you use timber be prepared to baby its whole life.
It will get dented easily, it will scratch easily, it will oxidise & change colour, but thats timber.
Some like it, some don't.