Understanding the Janka timber hardness scale for decking

Choosing the right timber for a deck often comes down to durability, workability and how the boards perform over time. You can also download and print our Janka hardness cheat sheet from this article to keep a quick reference on hand when specifying decking or talking clients through options.  

One of the most commonly referenced measures across the trade is the Janka hardness rating. This guide explains how the Janka hardness test works, what the ratings mean in practical terms and how installers typically use a wood hardness scale when selecting decking materials in Australia. 

The Janka test measures how resistant timber is to denting  

The Janka hardness test measures the force required to press a steel ball into timber to a standard depth. The more force required, the harder and denser the wood. The result is expressed as a Janka rating and allows different timber species to be compared on a consistent basis. 

In Australia, Janka ratings are usually considered alongside other performance factors such as durability class, termite resistance and Bushfire Attack Level (BAL) requirements. While the test itself focuses purely on surface hardness, it provides a practical reference point within the broader lumber hardness scale used across decking and flooring applications. 

Janka hardness helps match decking timber to performance and budget 

The Janka hardness scale used in Australia spans a wide range, from soft softwoods through to very dense Australian hardwoods. An Australian timber hardness chart typically shows decking species spread across this spectrum, from lighter timbers like Treated Pine through to high-density species such as Ironbark and Northern Box. 

Rather than being treated as pass or fail, Janka values are generally used as a guide to indicate resistance to denting, surface wear and long-term performance under foot traffic. The rating also hints at how demanding a timber may be during installation, particularly when it comes to cutting, drilling and fastening. 

In practice, Janka rating ranges guide timber choice on site  

Janka ratings are most useful when viewed in ranges rather than as individual numbers. The ranges below reflect common trade interpretation for decking in Australia. 

Less than 5.9 | Softer timbers
Lower ratings indicate softer timbers that are easier to cut, fix and finish. These species are typically used in low-traffic or covered applications and are often selected where affordability and ease of install are key considerations. 

6.0 to 8.9 | Medium hardness timbers
This range covers many popular residential decking options, offering a balance between workability and durability. 

Species such as Cypress Pine and Pacific Mahogany are often selected for family decks where everyday foot traffic is expected without moving into very hard hardwoods. 

9.0 to 11.9 | Hard timbers
Higher ratings indicate dense hardwoods designed to cope with frequent use, exposure and heavier foot traffic. 

Jarrah has a Janka rating of 8.5 and sits at the lower end of this transition into harder hardwoods, while species such as Spotted Gum NSW rate around 11.0 and are commonly specified where strength and durability are a priority. 

12.0+ | Very hard timbers 
Timbers in this range are selected for demanding environments, including heavy-use residential and commercial settings. 

Species such as Turpentine (12.0), Grey Ironbark (14.0) and Northern Box (14+) sit at the upper end of the wood hardness scale used by Australian installers and offer maximum resistance to wear and surface damage. 

Our timber hardness chart helps balance durability, install time and cost 

Our Janka timber hardness chart allows for quick comparison between species. When using these charts in practice, it helps to factor in: 

• Expected foot traffic and overall use 
• Exposure to weather and moisture 
• Installation time and impact on tools 
• Client expectations around long-term appearance 

Harder timbers tend to offer greater resistance to surface damage but can increase labour time and require pre-drilling. Softer timbers speed up installation and finishing but are better suited to lighter-duty applications. 

Download a copy of our Janka hardness cheat sheet here.

In summary 

• The Janka hardness test measures resistance to surface indentation 
• Janka ratings allow practical comparison between timber species 
• Higher ratings generally indicate greater wear resistance 
• Softer timbers improve workability and installation speed 
• Timber hardness is best matched to traffic levels, exposure and intended use 
• Download a copy of our Janka hardness cheat sheet here.

Abbey Timber has the largest range of decking timbers, composite decking, hardware, and tools, with fast delivery and a Sydney showroom where you can see the difference for yourself. 

If you would like more advice from one of the expert trade team at Abbey Timber, call or visit the showroom or chat to us online.