The Janka hardness test (;. ), created by Austrian-born American researcher Gabriel Janka (1864–1932), measures the resistance of a sample of wood to denting and wear. It measures the force required to embed an steel ball halfway into a sample of wood. (The diameter was chosen to produce a circle with an area of 100 square millimeters, or one square centimeter.)
A common use of Janka hardness ratings is to determine whether a species is suitable for use as flooring. For hardwood flooring, the test usually requires an sample with a thickness of at least 6–8 mm, and the most commonly used test is the ASTM D1037. When testing wood in lumber form, the Janka test is always carried out on wood from the tree trunk (known as the heartwood), and the standard sample (according to ASTM D143) is at 12% moisture content and clear of knots.
The hardness of wood varies with the direction of the wood grain. Testing on the surface of a plank, perpendicular to the grain, is said to be of "side hardness". Testing the cut surface of a stump is called a test of "end hardness". Side hardness may be further divided into "radial hardness" and "tangential hardness", although the differences are minor and often neglected.
The results are stated in various ways, leading to confusion, especially when the actual units employed are often not attached. The resulting measure is always one of force. In the United States, the measurement is in pounds-force (lbf). In Sweden, it is in kilograms-force (kgf), and in Australia, either in newtons (N) or kilonewtons (kN). This confusion is greatest when the results are treated as units, for example "660 Janka".
The Janka hardness test results tabulated below followed ASTM D 1037-12 testing methods. Lumber stocks tested range from 1" to 2" (25–50 mm) thick. The tabulated Janka hardness numbers are an average. There is a standard deviation associated with each species, but these values are not given. No testing was done on actual flooring.
Other factors affect how flooring performs: the type of core for engineered floorings, such as pine, HDF, poplar, oak, or birch; grain direction and thickness; floor or top wear surface, etc. The chart is not to be considered an absolute; it is meant to help people understand which woods are harder than others.
Typical Janka hardness values KeyHardwoodSoftwoodPseudowood + Typical Janka side hardnessSpecies Force: pounds-force (newtons) Australian Buloke Schinopsis brasiliensis, Quebracho, Barauna, Chamacoco Schinopsis balansae, Quebracho Colorado, Red Quebracho Lignum vitae, Guayacan, Pockholz Cornus mas Anadenanthera colubrina var. cebil, Curupay, Angico Preto, Brazilian Tiger Mahogany Snakewood, Letterhout, Brosimum guianense Brazilian Olivewood Brazilian Ebony Ipê, Brazilian Walnut, Handroanthus lapacho African Pearwood, Moabi Grey Ironbark Bolivian Cherry Lapacho Sucupira, Brazilian Chestnut, Tiete Chestnut Kingwood Dipteryx, Cumaru, Brazilian Teak Ironwood Ebony Massaranduba, Brazilian Redwood, Paraju Yvyraro Strand Woven Bamboo Cocobolo Bloodwood (Brosimum rubescens) Boxwood Olive Red Mahogany, turpentine Live Oak Southern Chestnut Spotted gum Brazilian Cherry, Jatoba Mesquite Golden Teak Guatambú, Kyrandy, Balfourodendron riedelianum Santos Mahogany, Bocote, Cabreuva, Honduran Rosewood Pradoo Brazilian Koa Brushbox Osage Orange Karri Sydney blue gum Palmyra Palm Bubinga Cameron Tallowwood Merbau Amendoim Jarrah Coconut Palm Purpleheart Goncalo Alves, Tigerwood Hickory, Pecan, Satinwood Afzelia, Doussie, Australian Wormy Chestnut Castello boxwood Bangkirai Rosewood Apple African Padauk Blackwood Merbau Kempas Black Locust Highland Beech Red Mulberry Wenge, Red Pine, Hornbeam Tualang Zebrawood True Pine, Timborana Peroba European Yew Sapele, Sapelli, Kupa'y Curupixa Sweet Birch Hard maple, Sugar Maple Caribbean Walnut Kentucky coffeetree Natural Bamboo (represents one species) Australian Cypress White Oak Tasmanian oak Ribbon gum Ash (White) American Beech Red Oak (Northern) Caribbean Heart Pine Keruing Yellow Birch, Iroko Movingui Heart pine Carapa guianensis, Brazilian Mesquite Larch Carbonized Bamboo (represents one species) Teak Brazilian Eucalyptus, rose gum English Oak Makore Siberian Larch Peruvian Walnut Boreal Black Walnut, North American Walnut Cherry Black Cherry, Imbuia Red Maple. Boire Paper Birch Eastern Red Cedar, Monkeypod Southern Yellow Pine (Longleaf) Lacewood, Leopardwood African Mahogany Mahogany, Honduran Mahogany Parana Sycamore Box Elder Shedua Radiata Pine Silver Maple Southern Yellow Pine (Loblolly and Shortleaf) Douglas Fir Western Juniper Alder (Red) Larch Chestnut Yellow Poplar, Poplar Hemlock Western White Pine Basswood Eastern White Pine Western Red Cedar Cuipo Balsa Balsa, softest wood ever measured: single unusual example The record softness of 22 lbf is often falsely ascribed to quipo, but all such reports appear to be a misreading of figures 15 and 16 from this primary source, which makes clear that measurement is of balsa, and the softest quipo measured was 46 lbf tangential, 38 lbf radial.
References
External links Janka Hardness Scale For Wood – Side Hardness Chart of Some Woods USDA – Wood Handbook – Wood as an Engineering Material USDA – Janka Hardness Using Nonstandard Specimens