Understanding Janka Ratings for Australian Hardwoods
If you’ve ever stepped into a timber yard or browsed flooring options in Australia, you’ve likely
encountered a mysterious number called the Janka rating.
Whether you’re a builder specifying materials for a high-traffic deck or a homeowner choosing the
perfect floorboards, understanding this rating is the key to ensuring your timber stands up to the
“thump and grind” of daily life.
What is the Janka Hardness Test?
The Janka rating isn’t a measure of how hard it is to break a piece of wood, but rather how resistant
it is to denting and wear.
The test is surprisingly literal: it measures the force required to embed an 11.28mm steel ball
halfway into a sample of timber. In Australia, this force is typically expressed in kilo-Newtons (kN).
The higher the number, the more force is required to dent the wood, meaning the timber is harder
and more durable against surface damage.
Why Does It Matter for Your Build?
In the building industry, the Janka rating influences three major factors:
Wear Resistance: High-traffic areas like hallways or commercial shopfronts need
“Hard” or “Very Hard” ratings to prevent damage from heavy footwear or furniture.
Workability: Generally, the harder the wood, the more it will “fight” back. Very hard
timbers often require pre-drilling and can blunt saw blades faster.
Longevity: While hardness doesn’t always equal rot resistance, a hard surface
keeps its “new” look longer by resisting scratches and gouges.
The Australian Hardwood Leaderboard
(Common Species)
| Timber Species | Janka Rating (kN) | Hardness Category | Common Uses |
| Grey Box | 15.0 | Very Hard | Structural beams, industrial floors |
| Grey Ironbark | 14.0 | Very Hard | Heavy-duty decking, commercial flooring |
| Turpentine | 12.0 | Very Hard | Marine piles, heavy-use flooring, decking |
| Tallowwood | 11.0 | Hard | High-end decking, flooring, bridge timber |
| Spotted Gum | 11.0 | Hard | Decking, flooring, cladding |
| Brush Box | 9.5 | Hard | Feature flooring, cladding, paneling |
| Blackbutt | 9.1 | Hard | General construction, flooring, framing |
| Sydney Blue Gum | 9.0 | Hard | Flooring, furniture, heavy construction |
| Karri | 9.0 | Hard | Heavy construction, flooring, framing |
| Jarrah | 8.5 | Medium-Hard | Feature flooring, high-end decking, joinery |
| Red Mahogany | 8.0 – 12.0 | Hard | External cladding, flooring, decking |
| Victorian Ash | 4.5 – 5.5 | Medium-Soft | Internal joinery, stairs, light-use flooring |
| Tasmanian Oak | 4.5 – 5.5 | Medium-Soft | Internal joinery, light-use flooring |
Choosing the Right Rating for Your Project
Choosing a timber is always a balancing act between aesthetics, cost, and performance. Here’s a
quick guide on where to aim on the Janka scale:
Low Traffic / Internal (4.0 – 7.0 kN): Species like Tasmanian Oak or Victorian Ash
are beautiful and easy to work with. Perfect for bedrooms where people are usually
barefoot.
Residential Flooring (8.0 – 11.0 kN): This is the “sweet spot.” Blackbutt and
Spotted Gum provide excellent protection against kids and pets without being
impossible to install.
External Decks & Commercial (12.0+ kN): For public boardwalks or party decks,
Ironbark or Turpentine are the gold standards.
A Quick Reality Check: While the Janka rating is a fantastic guide, remember that it
measures the timber itself. If you are installing a timber floor, the type of coating
(polyurethane vs. oil) also plays a massive role in scratch resistance.