What Janka hardness actually measures
The Janka hardness test measures the force (in pounds-force, lbf) required to embed a 0.444" steel ball halfway into a piece of wood. Higher numbers = harder wood.
The test was developed for flooring — harder wood resists denting from foot traffic. But "hard" doesn't always mean "better." For a cutting board, very hard wood (like ebony) dulls knives fast. For a workbench top, you want hard to resist dings from clamps and tools.
Janka hardness by category
- Under 500 lbf (very soft): Balsa, cedar, pine, paulownia
- 500-1000 lbf (soft to medium): Poplar, cherry, walnut, soft maple
- 1000-1500 lbf (medium hard): Red oak, hard maple, ash, beech, teak
- 1500-2000 lbf (hard): White oak, hickory, hard maple, bamboo (carbonized)
- 2000-3000 lbf (very hard): Wenge, bubinga, purpleheart, ipe
- 3000+ lbf (extremely hard): Lignum vitae, ebony, snakewood
What the numbers predict (and don't)
Janka predicts:
- Dent resistance (floors, workbench tops, cutting boards)
- Wear resistance (chair arms, table edges)
- Tool wear (harder wood dulls tools faster)
- Sanding difficulty (harder wood requires more aggressive abrasives)
Janka doesn't predict:
- Bending strength (different test — modulus of elasticity)
- Stiffness (different test)
- Decay resistance (depends on extractives, not hardness)
- Stability / movement (depends on species, grain orientation)
- Workability (also depends on grain, silica content, etc.)
Janka by project
- Flooring (high wear): 1200-2500 lbf ideal. Hard enough to resist dents, soft enough to finish without extreme tooling.
- Cutting boards: 500-1500 lbf sweet spot. Too hard dulls knives; too soft cuts easily. Cherry and hard maple are the standards.
- Cabinetry: 500-1500 lbf. Soft enough to machine easily, hard enough to resist dings.
- Furniture: 700-1500 lbf. Match the wear expectation — bedroom furniture less than kitchen tables.
- Musical instruments: Specific resonance properties matter more than hardness. Spruce for tops (low Janka), maple for backs (medium).
Why hardness changes with moisture
Wood at 12% MC is roughly 1.5× harder than wood at 0% MC. At 20% MC, it's about 0.6× as hard. The Janka test is standardized at 12% MC for fair comparison.
Practical implication: don't compare green wood Janka values to dry wood values. They're not the same test.
Side hardness vs end hardness
The standard Janka test is done on the side (face grain) of the board. End-grain Janka values are typically 20-30% higher because end grain is more compressed. We list side-grain values here.
How Janka compares to other tests
- Brinell hardness: Used for metals. Higher numbers, different units (HB).
- Rockwell hardness: Also for metals (HRC).
- Mohs hardness: Mineral scale (1-10). Wood rates around 1-4.
- Shore D: Plastic scale.
Janka is the wood-specific standard. Don't try to convert between scales.
Frequently asked questions
Is harder wood always better?
No. Harder wood is harder to work, dulls tools faster, and is more difficult to sand and finish. Choose hardness for the project's needs, not because more is always better.
What about engineered wood?
Plywood, MDF, and laminate have no Janka rating in the same sense — they're composites. Bamboo flooring has Janka values comparable to hardwood.
How does finish affect hardness?
Film finishes (poly, lacquer) add some scratch resistance but not much. Hardwax oil soaks in but doesn't add hardness. For high-wear surfaces, choose hard wood first, finish second.