This number is incredibly useful in directly determining how well a wood will withstand dents, dings, and wear—as well as indirectly predicting the difficulty in nailing, screwing, sanding, or sawing a given wood species.

Janka hardness testing

Janka hardness testing

The actual number listed in the wood profile is the amount of pounds-force (lbf) or newtons (N) required to imbed a .444″ (11.28 mm) diameter steel ball into the wood to half the ball’s diameter. This number is given for wood that has been dried to a 12% moisture content, unless otherwise noted.

For reference, White Oak has a Janka hardness of 1,360 lbf (6,000 N), while the super-hard Lignum Vitae has a hardness of an astounding 4,500 lbf (20,000 N). (Who could imagine a wood species that is over three times harder than White Oak?) On the lower end of the spectrum, Basswood has a hardness of around 410 lbf (1,800 N).

hardness

Also, in some instances, I’ve estimated the Janka hardness value using equations that use the wood’s basic specific gravity, as found in the paper, “Estimating Janka Hardness from Specific Gravity for Tropical and Temperate Species.”

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  • stephensaugnier

    I had a question – At what measure of hardness is a wood classified as a hardwood or softwood? Is there a specific threshold?

    • ejmeier

      Hardwood and softwood labels are somewhat misleading, and have nothing actually to do with the hardness of the wood, but rather to botany. Angiosperms are referred to as hardwoods, while gymnosperms (aka conifers) are softwoods. Technically Balsa is a hardwood, though it’s the softest wood around, and some softwoods can be somewhat hard. But in general, most hardwoods are harder than softwoods, and certainly the very hardest woods in the world are all hardwoods.

      • stephensaugnier

        That’s a great explanation Ejmeier. Thank you for clarifying. I had a query with regards to Douglas Fir wood. It has a Janka hardness of 660 lb which technically makes it a softwood but a lot of people vouch for its durability. So just wanted to check with you too..thoughts?

        • ejmeier

          I suppose it depends on what you’re comparing it to. Douglas fir is probably above average in hardness for a softwood, but I’d say that it was by no means as tough as something like oak or hard maple. But going back to your original question in terms of a hardness threshold, it depends on the application, but for me, I’d look for at least a Janka hardness of say around 800 or 900 lbf for most objects that will get handled, etc., and closer to 1500 lbf for things like worktops or flooring.

        • BPS

          Douglas fir works out great for wood working benches. Having to hard of a surface on your bench can cause marks in your work. It is a question of whether you want the marks to show up on your new piece of work or on the work bench. Douglas fir provided a good stable surface to work on.

  • Muzzled ?????? ?????????

    We are install solid wood/sand poly floor in a new home with a full basement, what vapor barrier should we use

  • ejmeier

    Well, the two standbys are White Ash and Hard Maple, so I would try to stay in that ballpark. Roughly, I would try to stay around the 1200 lbf mark. But as you said, there are a lot of other properties that are more important than hardness, one of which is shock resistance.