Hardness sounds simple — how well does this timber resist being dented? But the answer matters every time you choose flooring, a benchtop, a cutting board, or a handrail. The Janka test gives you a single number to compare species — and once you understand what it measures and what it misses, you’ll use it with confidence.
In Guide 1, we covered density — the most informative single number about any timber species. We noted that density and hardness are strongly correlated: more cell wall material per unit volume means more resistance at the surface.
This guide zooms in on that relationship and explores the standard test used worldwide to measure timber hardness: the Janka hardness test.
What Hardness Means in Timber
Hardness is a material’s resistance to indentation — its ability to resist a localised force pressing into its surface.
In metals, hardness is tested with sharp points (Vickers, Rockwell). In timber, the standard method uses a steel ball pressed into the wood surface. This is the Janka test.
Hardness matters whenever timber meets wear, impact, or pressure:
- Flooring — foot traffic, furniture legs, dropped objects
- Benchtops — tools, clamps, heavy components
- Furniture surfaces — everyday use, scratches, dents
- Handrails and stairs — constant contact and grip wear
- Outdoor decking — furniture, foot traffic, weather
A timber that dents easily will show every knock. A timber that resists denting will look better for longer — but may be harder to work.
The Janka Hardness Test
The Janka test was developed by Austrian-born researcher Gabriel Janka in the early 1900s. It remains the global standard for comparing timber hardness.
How it works
A steel ball with a diameter of 11.28 mm is pressed into the surface of a timber sample. The ball is pushed in until it has penetrated to exactly half its diameter — meaning the indentation has a projected area of exactly 100 mm².
The force required to achieve this penetration is recorded.
That force — measured in Newtons (N) or sometimes pounds-force (lbf) — is the Janka hardness rating.
$$ \text{Janka hardness} = \text{Force to embed an 11.28 mm ball to half its diameter} $$
Why a ball?
A ball creates a consistent, repeatable indentation regardless of grain direction at the contact point. Unlike a sharp point (which could slip between fibres) or a flat plate (which wouldn’t create a localised impression), the ball gives a reliable average response from the wood surface.
Side hardness vs end hardness
The Janka test can be performed on two faces:
- Side hardness — the ball is pressed into the face or edge grain (the surfaces you normally see in boards). This is the standard value reported for most practical purposes.
- End hardness — the ball is pressed into the end grain. End hardness is typically much higher (often 40–70% higher) because the ball is pressing against the ends of the wood fibres rather than across them.
When you see a Janka value on a species data sheet or flooring specification, it is almost always the side hardness unless stated otherwise.
Janka Ratings for Common Species
Here are approximate Janka side hardness values at ~12% moisture content:
| Species | Janka Hardness (N) | Janka Hardness (lbf) | Category | | — | — | — | — | | Balsa | 300 | 67 | Extremely soft | | Western Red Cedar | 1,600 | 350 | Soft | | Scots Pine | 2,200 | 490 | Soft–Medium | | Douglas Fir | 2,400 | 540 | Medium | | Black Walnut | 4,500 | 1,010 | Medium | | American Cherry | 4,200 | 950 | Medium | | European Oak | 5,400 | 1,220 | Hard | | European Ash | 5,600 | 1,260 | Hard | | Hard Maple | 6,400 | 1,450 | Hard | | European Beech | 6,500 | 1,450 | Hard | | Hickory | 8,100 | 1,820 | Very hard | | Ipe | 15,600 | 3,510 | Extremely hard | | Lignum Vitae | 20,000+ | 4,500+ | Extraordinarily hard |
The range is enormous. Lignum vitae is roughly 65 times harder than balsa. Even within commonly used workshop species, hard maple is roughly four times harder than western red cedar.
The Relationship Between Density and Janka Hardness
As we previewed in Guide 1, density and Janka hardness are strongly correlated.
This makes intuitive sense. A denser species has more cell wall material at the surface. When a steel ball is pressed into the wood, there is more solid material resisting the intrusion.
If you plotted density (x-axis) against Janka hardness (y-axis) for hundreds of species, you would see a clear upward trend — not a perfect line, but a strong one.
The general rule
- Below ~450 kg/m³: Soft, dents easily. Suitable for light-wear surfaces or non-contact applications.
- 450–600 kg/m³: Medium hardness. Acceptable for furniture, moderate-traffic flooring.
- 600–750 kg/m³: Hard. Good for most flooring and high-use furniture.
- Above 750 kg/m³: Very hard. Excellent wear resistance. Harder to work.
Why it’s not a perfect line
Some species are harder or softer than their density alone would predict:
- Teak (~640 kg/m³) has a Janka rating slightly lower than expected — its oily extractives make it naturally slippery under the ball
- Hickory (~750 kg/m³) tests harder than expected — its long, interlocking fibres resist indentation exceptionally well
- Radiata Pine (~480 kg/m³) has a wide variation in hardness because of extreme density differences between earlywood and latewood bands
Density gets you close. But the specific cell arrangement, fibre length, extractive content, and grain pattern all influence the final number.
Units and Conversions
Janka hardness values appear in different units depending on the source:
- Newtons (N) — the SI standard, used in most international and scientific sources
- Pounds-force (lbf) — used extensively in the United States and in American species databases
- Kilogram-force (kgf) — occasionally used in older European references
Conversion:
$$ 1 \text{ lbf} \approx 4.45 \text{ N} $$
$$ 1 \text{ kgf} \approx 9.81 \text{ N} $$
<aside> ⚠️
When comparing Janka values between sources, always check the units. A value of 1,450 in lbf (Hard Maple) looks very different from 6,400 in Newtons — but they describe the same timber. Mixing units is one of the most common mistakes in species comparisons.
</aside>
Janka Hardness and Flooring
The most common real-world application of the Janka rating is flooring selection.
Flooring takes more surface abuse than almost any other timber application: foot traffic, chair legs, dropped objects, pet claws, grit, and furniture being dragged across it.
General flooring guidelines
| Use case | Minimum Janka (N) | Example species | | — | — | — | | Low-traffic rooms (bedroom, study) | ~3,500 | Walnut, Cherry | | Medium-traffic areas (living room, dining) | ~5,000 | Oak, Ash | | High-traffic areas (hallway, kitchen) | ~6,000 | Maple, Beech | | Commercial or heavy-use | ~8,000+ | Hickory, Jarrah, Ipe |
These are guidelines, not rules. A well-finished, well-maintained cherry floor can perform beautifully in a living room. And many people prefer the character that soft dents bring to a pine floor over time.
The character argument
Not everyone wants the hardest possible floor. Some woodworkers and homeowners actively choose softer species — pine, Douglas fir, larch — because they develop a patina of use: gentle dents, wear patterns, and surface texture that tell the story of the room.
This is a legitimate design choice. The Janka number tells you what will happen, not what should happen. The right hardness depends on the application, the finish, and the owner’s expectations.
Hardness Variation Within a Board
Janka values are averages. Within a single board, hardness can vary significantly.
Earlywood vs latewood
In ring-porous species (oak, ash), the earlywood band contains large, open pores — and is noticeably softer than the dense latewood. If you press your fingernail into the face of an oak board, the earlywood dents more easily.
This difference is visible in flooring wear: over decades, the softer earlywood erodes slightly faster than the latewood, creating a subtle textured surface.
Growth ring orientation
Quarter-sawn boards present a different surface to wear than plain-sawn boards. In quarter-sawn timber, the growth rings run roughly perpendicular to the face — meaning both earlywood and latewood are exposed in thin, even stripes. This often produces more uniform wear.
Plain-sawn boards present wider bands of earlywood and latewood, which can wear unevenly.
Juvenile wood vs mature wood
Wood near the pith (juvenile wood) is typically softer than mature wood further from the centre of the tree. A board containing a mix of juvenile and mature wood may test differently at different points.
Moisture Content and Hardness
Like density, Janka hardness is affected by moisture content.
Drier timber is harder. As wood loses moisture below the fibre saturation point (~28–30% MC), the cell walls contract and stiffen. This makes the wood more resistant to indentation.
Wetter timber is softer. Above the fibre saturation point, the extra water in the cell walls acts as a plasticiser, making the wood more easily deformed.
Standard Janka values are reported at ~12% MC (air-dry). If you’re testing timber at a different moisture content, your results won’t be directly comparable to published values.
<aside> 📌
Practical implication: If you’re installing a hardwood floor and the boards arrive wetter than expected, they will be slightly softer than their rated Janka value. Once they equilibrate to indoor conditions (~8–12% MC), they’ll reach their full rated hardness.
</aside>
How to Think About Janka in the Workshop
You won’t run a Janka test on your workbench. But the concept is useful every day.
Choosing a workbench top
A bench needs to resist denting from tools, clamps, and workpieces — but not be so hard that it damages the work. European beech (Janka ~6,500 N) is the traditional choice: hard enough to resist casual dents, soft enough not to mar fine workpieces.
Choosing cutting boards
A cutting board that’s too hard (maple, beech) will dull knives faster. A board that’s too soft (pine) will show deep cut marks quickly. Many makers target the middle range — walnut, cherry — as a compromise between knife-friendliness and durability.
Predicting finish quality
Harder timber generally takes a smoother, more polished finish. The surface is less likely to show sanding scratches or absorb finish unevenly. Softer timber may need more preparation to achieve the same result.
Anticipating tool wear
Very hard timber dulls blades, bits, and chisels faster. If you’re machining ipe or jarrah, expect to sharpen more often than when working with cedar or pine.
Limitations of the Janka Test
The Janka number is useful, but it doesn’t tell the whole story about how a timber surface performs.
It measures static indentation, not impact
The Janka test pushes a ball in slowly. It doesn’t simulate a hammer dropping on a floor or a chair leg slamming down. Impact resistance depends on other factors — particularly toughness (the ability to absorb energy without fracturing).
Some hard species are also brittle. Ipe resists denting superbly, but a sharp impact on the end grain can cause it to chip. Ash, while slightly softer, absorbs shock better — which is why it’s traditionally used for tool handles.
It doesn’t measure scratch resistance
A Janka test presses a smooth ball into wood. Scratches are caused by sharp or gritty objects dragging across the surface — a different mechanism. Finish type, grain density, and extractive content all affect scratch resistance independently of Janka hardness.
It doesn’t account for finish
A well-applied polyurethane or hardwax oil finish can significantly improve the surface performance of a softer timber. A poorly finished hard timber may perform worse in practice than a well-finished medium timber.
It averages across the surface
As noted above, hardness varies within a board. The Janka number is an average — it doesn’t capture the difference between the soft earlywood and hard latewood in a ring-porous species.
Alternative Hardness Tests
The Janka test is dominant in the timber world, but other methods exist:
- Brinell hardness — uses a larger steel ball and is common in European flooring standards. Results are reported in MPa or N/mm². Brinell values are not directly comparable to Janka values.
- Monnin (Chalais-Meudon) — a French method historically used for European species. Less common today.
- Rockwell and Vickers — used primarily for metals but occasionally applied to very hard, dense timbers or wood composites.
For most practical purposes in woodworking and timber selection, Janka is the standard you’ll encounter.
Media and Image Recommendations
- Photo: the Janka test in action
- A steel ball being pressed into a timber sample on a testing machine — shows the physical setup clearly
- Diagram: side hardness vs end hardness
- Simple cross-section of a board showing where each test is applied and why end grain is harder
- Chart: density vs Janka scatter plot
- Plot common species with density on the x-axis and Janka on the y-axis — showing the strong but imperfect correlation
- Photo comparison: dent resistance
- Same steel ball dropped from the same height onto pine, oak, and ipe — showing the resulting dent sizes side by side
- Flooring wear comparison
- Close-up photos of pine flooring vs oak flooring vs maple flooring after equivalent wear periods
The Key Idea
<aside> 💡
The Janka hardness test gives you a reliable, comparable number for how well a timber species resists denting. It’s closely tied to density, widely used in flooring and furniture decisions, and the most practical hardness measure in the timber world. But remember — it measures one type of resistance. Scratch resistance, impact toughness, and finish all play their part too.
</aside>
What’s Next
In Guide 3 — Strength vs Stiffness (MOE vs MOR), we move beyond surface properties and into the structural heart of timber. How much load can a beam carry before it breaks? How much does it bend under load? These two measures — Modulus of Rupture and Modulus of Elasticity — are essential for anyone using timber structurally, and they relate to density in ways that will now feel familiar.
🔗 Knowledge Network
Species Pages
- Balsa — extremely soft (Janka ~300 N)
- Western Red Cedar — soft (Janka ~1,600 N)
- Scots Pine — soft–medium (Janka ~2,200 N)
- Douglas Fir — medium (Janka ~2,400 N)
- Black Walnut — medium (Janka ~4,500 N)
- American Cherry — medium (Janka ~4,200 N)
- European Oak — hard (Janka ~5,400 N)
- European Ash — hard (Janka ~5,600 N)
- Hard Maple — hard (Janka ~6,400 N)
- European Beech — hard (Janka ~6,500 N)
- Hickory — very hard (Janka ~8,100 N)
- Ipe — extremely hard (Janka ~15,600 N)
Glossary Terms
- Janka Hardness
- Indentation Resistance
- Side Hardness
- End Hardness
- Brinell Hardness
- Earlywood vs Latewood (hardness variation)
Calculators
- None for this guide
Related Guides
- Track 3 – Guide 3 – Strength vs Stiffness (MOE vs MOR) — the structural properties that complement surface hardness
- Track 3 – Guide 6 – Workability of Timber — how hardness affects tool response
- Track 1 – Guide 3 – Hardwood vs Softwood — structural differences driving hardness
- Track 1 – Guide 5 – Growth Rings Explained — earlywood/latewood hardness variation
- Track 4 – Guide 2 – Plain Sawn vs Quarter Sawn vs Rift Sawn — how cut angle affects surface wear patterns