When buying wood, you may have come across the term Janka hardness, or read about this wood hardness scale in one of my previous articles. But what is Janka rating, and how is the Janka hardness rating expressed?
A Janka rating is a classification that indicates the hardness of wood expressed in Newtons (N) or pounds-force (lbs.). Janka hardness rating is largely used by the wooden flooring industry, but can also determine the choice of wood for your projects.
In this concise article I not only answer the question “what is janka rating”, but I also take a closer look at how it is measured and, more importantly, whether this technique is still applicable to the wood we use today. Find out all about it in this intriguing explanation with a surprising outcome.
- What is Janka rating?
- What is a good Janka rating?
- Is the Janka rating still relevant?
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What is Janka rating?
Who Created the Janka Rating?
The Janka system was named after an Austrian named Gabriel Janka, who worked for the Forest Products Lab of the United States Department of Agriculture (USDA).
After being tasked by the Department with scientifically measuring the hardness of U.S. hardwoods, he developed the wood rating scale that is now used around the world. The Janka hardness test method has since been formalized by the American Society for Testing and Materials (ASTM).
Similar indentation hardness tests are used throughout engineering to determine the hardness of various materials. Understanding the wood hardness scale allows manufacturers to determine how much wear and tear various materials can withstand, as well as the applications in which they can be used, allowing them to create high-quality tools, building materials, and other products.
How do you test Janka hardness?
A Janka rating is a rating used primarily by the timber flooring industry to compare the hardness of wood. It is the primary test for determining the wear and deniability of wood. So, how do you determine Janka hardness?
Pushing an 11.18 mm (0.44 inch) diameter steel ball into wood fiber until it reaches half its diameter is the Janka hardness test method. The applied force is then measured in Newtons (N) or pounds-force (lbs.) as the Janka rating.
The more force required, the higher the Janka score and the more durable the wood. also good to know is that this number is given for wood that has been dried to a 12% moisture content, unless otherwise noted.
Testing Janka hardness, as you can see, necessitates the use of specialized equipment. This is something that can only be done in specialized labs. You don’t need to test this, however, because you can find Janka hardness scale charts on the internet that will tell you the hardness of the wood. I always use the wood database for this.
What is the purpose of the Janka scale?
This wood hardness scale is primarily used as a sales technique to promote the dent resistance of wood in comparison to other materials, particularly on wood floors. Although it is frequently confused with impact resistance (measured in Joules), this is incorrect.
The growing popularity of flooring terminology can be attributed to marketing used by companies selling high-density hardwood floors, who are presumably looking for a tradable difference from traditional volumetric wood flooring markets.
The hardness of wood will play a role in durability. However, to determine the durability of wood, there are other factors on which the wood is tested. To learn more about wood durability and the different durability classes, I recommend reading my article, A Clear Guide To Durability Classes Of Wood + Chart.
What is a good Janka rating?
A Janka rating of 4,448 N (1,000 lbs.) or higher is considered a good Janka rating for wood floors. The industry standard is approximately 5,337 N (1,200 lbs.)
It is critical to consider the applications of wood when selecting it. A wood type with a high Janka score is preferable for projects that will be subjected to a lot of wear and tear. Teak, for example, has a Janka rating of 4,448 N (1,000 lbs.), while maple has a Janka rating of 6,449 N (1,450 lbs.).
It’s also worth noting that, regardless of Janka rating, all woods are prone to dents and wear under the wrong conditions. In addition, a high Janka score may not be the most important factor.
For your info, I’ll provide some Janka rankings of the most commonly used woods in woodworking. These are the woods that are commonly used to make furniture, cutting boards, and other items.
|Linden / basswood||1,820||410|
What wood has the highest Janka rating?
You saw earlier in this article that wood can have its hardness quantified using the Janka classification. This rating measures the resistance of wood samples to dents and wear.
To give you an overview, below you will find a list of the 10 hardest kinds of wood in the world, along with some information about each type.
1 QUEBRACHO (Schinopsis spp.) – 20,340 N (4,570 lbs.)
The term “axe breaker” comes from the Spanish “quebrar hacha.” Wood from the Schinopsis genus is among the world’s heaviest and hardest woods.
2 LIGNUM VITAE (Guaiacum officinale) – 19,510 N (4,390 lbs.)
This wood is widely regarded as the hardest woods in the world, and CITES has listed it as an endangered species. Verawood is a reasonable substitute.
3 GIDGEE (Acacia cambagei) – 18,990 N (4,270 lbs.)
This endemic from Australia is both powerful and heavy. Some pieces are dark enough to be mistaken for ebony, which is even harder than the original.
4 SNAKEWOOD (Brosimum guianensis) – 16,900 N (3,800 lbs.)
Snakewood’s patterns and markings are eerily similar to snake skin, which explains why it’s so distinctive. This is one of the most expensive woods on the planet due to scarcity and high demand!
5 VERAWOOD (Bulnesia arborea) – 16,520 N (3,710 lbs.)
This wood, also known as Argentine Lignum Vitae, is a gem: it’s inexpensive, has a great olive-green color, a beautiful feathery grain pattern, and it takes a great natural polish on the lathe.
6 CAMELTHORN (Vachellia erioloba) – 16,370 N (3,680 lbs.)
This South African hardwood, formerly classified as a member of the Acacia genus, is a tough customer. The wood is tenaciously hard, and the tree is guarded by massive sharp thorns.
7 AFRICAN BLACKWOOD (Dalbergia melanoxylon) – 16,320 N (3,670 lbs.)
This wood has almost legendary status in some parts of the world. This wood (rather than Diospyros spp.) is thought to be the original “ebony” according to historical evidence.
8 BLACK IRONWOOD (Krugiodendron ferreum) – 16,280 N (3,660 lbs.)
Because this tree is too small to produce commercially viable lumber, pieces are rarely seen for sale. Black Ironwood, like the unrelated Desert Ironwood, is an excellent choice for small turning projects.
9 KATALOX / WAMARA (Swartzia spp.) – 16,260 N (3,655 lbs.)
Some pieces are as dark as true ebony, while others are more reddish brown with black streaks. There is so much variety in the Swartzia genus that there is something for everyone!
10 CEBIL (Anadenanthera colubrina) – 16,150 N (3,630 lbs.)
Cebil, also known as Curupay or the overstated name Patagonian Rosewood, is not a true rosewood. It has a streaked appearance that is similar to Goncalo Alves.
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What is the softest wood on the Janka scale?
10 WESTERN RED CEDAR (Thuja plicata) – 1,560 N (350 lbf.)
This softie is a common soundboard material on guitars, but its softness makes it difficult to handle properly during construction without denting or gouging it.
9 BLACK COTTONWOOD / QUAKING ASPEN (Populus tremuloides and P. trichocarpa) – 1,560 N (350 lbf.)
These two woods are related and have similar Janka hardness values. Aspen is occasionally used for utility lumber.
8 ATLANTIC WHITE CEDAR (Chamaecyparis thyoides) – 1,560 N (350 lbf.)
Southern White Cedar is sometimes used to distinguish it from Northern White Cedar, which has the same Janka hardness value.
7 YELLOW BUCKEYE (Aesculus octandra) – 1,560 N (350 lbf.)
Burl sections are decorative and used for electric guitars and small specialty wood objects, whereas lumber is sometimes used for utility wood.
6 SUBALPINE FIR (Abies lasiocarpa) – 1,560 N (350 lbf.)
Many Fir (Abeis genus) species are soft, with Subalpine Fir being the softest, second only to European Silver Fir.
5 NORTHERN WHITE CEDAR (Thuja occidentalis) – 1,560 N (350 lbf.)
Northern White Cedar, which is closely related to Western Red Cedar, is one of the softest cedars and one of the softest conifers.
4 EUROPEAN SILVER FIR (Abies alba) – 1,420 N (320lbf.)
Not only is European Silver Fir the softest of the Fir species (Abies genus), but it is also one of the softest of the softwoods. The remaining woods on this list are all hardwoods.
3 BALSAM POPLAR (Populus balsamifera) – 1,330 N (300 lbf.)
When young, Balsam Poplar, a relative of Cottonwood and Aspen, has a distinct scent, but it dries to be one of the lightest and softest woods.
2 PAULOWNIA (Paulownia spp.) – 1,160N(260 lbf.)
Balsa, on the other hand, is a wood. Paulownia can be very light and soft, and is the only other wood that can sometimes compete with Balsa’s lightness. Both are, ironically, hardwoods.
1 BALSA (Ochroma pyramidale) – 390 N (90 lbf.)
Balsa wood is the softest and lightest commercial wood on the market. Nothing else even comes close. This material can be used for insulation, buoyancy, and a variety of other specialized applications.
Is the Janka rating still relevant?
Janka hardness rating is still a widely used scale, but it is no longer relevant in some industries, such as the wood flooring industry. That is why the Australian Timber Flooring Association (ATFA) proposed a shift in how we think about flooring hardness and then created a table with groups of Soft – Moderately Hard – Hard – Very Hard.
But, even if you’re a DIYer, looking at the Janka shell isn’t enough; there’s more to consider than hardness when selecting a suitable wood type.
Reasons why Janka ratings are not relevant
We use wood in a different way
Janka is not relevant to the flooring industry because it is irrelevant to the test when a Janka rating is used on a veneer or wood thickness less than 6 mm (0.23 inches). This applies to composite or reconstituted wood floors.
Despite the fact that the Janka classification recommended for these products is almost always based on historical records for the species in its solid form. Because most floors are now made of multiple materials, the Janka classification is no longer applicable.
Janka’s data is out of date.
The Janka rates recommended are largely based on historical data from primeval wood. Today, regrowth and plantation wood dominate the supply chain. Independent tests on this wood at Australian universities reveal that it is no longer as hard as historical data suggests.
Janka’s classification can be misleading.
Janka hardness ratingreflects dent resistance in wood, but it is only one aspect of wood’s durability. Wood’s overall performance comprises scratch resistance, dent resistance, stability, longevity, and recoverability. As a result, the Janka classification alone is insufficient.
Focusing on just the Janka assessment diverts attention from these other critical and more problematic issues. In reality, a balance of stability, longevity, durability, and long-term serviceability is what you should be looking at.
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