A measure of the hardness of wood, produced by a variation on the Brinell hardness test. The test measures the force required to push a steel ball with a diameter of 11.28 millimeters (0.444 inches) into the wood to a depth of half the ball's diameter (the diameter was chosen to produce a circle with an area of 100 square millimeters). In Janka's original test. the results were expressed in units of pressure, but when the ASTM standardized the test (tentative issue in 1922 , standard first formally adopted in 1927 ), it called for results in units of force.

The results are stated in various ways in different countries, which can lead to confusion, especially since the name of the actual unit employed is often not attached. In the United States, the measurement is in pounds-force. In Sweden it is apparently in kilogram-force (kgf), and in Australia, Janka hardness ratings are either in newtons (N) or kilonewtons (kN). Sometimes the results are treated as units, e.g., "360 janka."

The hardness of wood usually varies with the direction of the grain. If testing is done on the surface of a plank, with the force exerted perpendicular to the grain, the test is said to be of "side hardness."  Side hardnesses of a block of wood measured in the direction of the tree's center (radially), and on a tangent to the tree's rings (tangentially), are typically very similar. End testing is also sometimes done (that is, testing the cut surface of a stump would be a test of end hardness).  The side hardness of teak, for example, is in the range 3730 to 4800 newtons, while the end hardness is in the range 4150 to 4500 newtons.

The most common use of Janka hardness ratings is to determine whether a species is suitable for use as flooring.

Common name	Scientific name	side hardness, Janka test, at 12% moisture content
		kilonewtons	pounds-force
afromosia	Pericopsis elata	7.1	1560
albarco	Cariniana spp.	4.5	1020
alder, red	Alnus rubra	2.6	590
alder, white	Alnus rhombifolia
andiroba	Carapa guianensis	5.0	1130
angelin	Andira inermis	7.8	1750
angelique	Dicorynia guianensis	5.7	1290
apple	Malus sylvestris	7.7	1730
ash, black	Fraxinus nigra	3.8	850
ash, blue	Fraxinus quadrangulata	9.0	2030
ash, green	Fraxinus pennsylvanica	5.3	1200
ash, oregon	Fraxinus latifolia	5.2	1160
ash, pumpkin	Fraxinus profunda	4.4	990
ash, white	Fraxinus americana	5.9	1320
aspen, bigtooth	Populus grandidentata	1.9	420
aspen, quaking	Populus tremuloides	1.6	350
avodire	Turraeanthus africanus	4.8	1080
azobe	Lophira aiata	14.9	3350
baldcypress	Taxcodium distichum	2.3	570
balsa	Ochroma pyramidale
banak	Virola spp.	2.3	510
basswood, American	Tilia americana	1.8	410
basswood, Carolina	Tilia caroliniana
basswood, white	Tilia heterophylla
beech, American	Fagus grandifolia	5.8	1300
benge	Guibourtia amoldiana	7.8	1750
birch, gray	Betula populifolia	3.4	760
birch, paper	Betula papyrifera	4.0	910
birch, river	Betula nigra
birch, sweet	Betula lenta	6.5	1470
birch, yellow	Betula alleghaniensis	5.6	1260
boxelder	Acer negundo	3.2	720
bubinga	Guibourtia spp.	12.0	2690
buckeye, Ohio	Aesculus glabra
buckeye, yellow	Aesculus octandra	1.6	350
buckthorn, cascara	Rhamnus purshiana	4.6	1040
bulletwood	Manilkara bidentata	14.2	3190
butternut	Juglans cinerea	2.2	490
buttonwood	Conocarpus erectus
catalpa, northern	Catalpa speciosa	2.4	550
catalpa, southern	Catalpa bignonioides	2.4	550
cativo	Prioria copaifera	2.8	630
cedar, Alaska	Chamaecyparis nootkatensis	2.6	580
cedar, atlantic white	Chamaecyparis thyoides	1.6	350
cedar, Port Orford	Chamaecyparis lawsoniana	3.2	720
cedar, yellow		2.6	580
ceiba	Ceiba pentandra	1.1	240
cherry, black	Prunus serotina	4.2	950
chestnut, American	Castenea dentata	2.4	540
chinkapin, giant	Castanopsis chrysophylla	3.2	730
coffeetree, Kentucky	Gymnocladus dioicus	6,2	1390
cottonwood) balsam poplar	Populus balsamifera	1.3	300
cottonwood, black	Populus trichocarpa	1.6	350
cottonwood, eastern	Populus deltoides	1.9	430
courbaril	Hymenaea courbaril	10.5	2350
cuangare	Dialyanthera spp.	1.7	380
cypress, Mexican	Cupressus lustianica	2.0	460
degame	Calycophyllum candidissimum	8.6	1940
determa	Ocotea rubra	2.9	660
dogwood, flowering	Cornus florida	9.6	2150
Douglas-fir, coast	Pseudotsuga menziesii	3.2	710
Douglas-fir. interior west	Pseudotsuga menziesii	2.9	660
Douglas-fir, interior north	Pseudotsuga menziesii	2.7	600
Douglas-fir, interior south	Pseudotsuga menziesii	2.3	510
ekop	Tetraberlinia tubmaniana
elder, blue	Sambucus cerulea	3.7	840
elm, american	Ulmus americana	3.7	830
elm, cedar	Ulmus crassifolia	5.9	1320
elm, rock	Ulmus thomasii	5.9	1320
elm, slippery	Ulmus rubra	3.8	860
elm, winged	Ulmus alata	6.8	1540
fir, balsam	Abies balsamea	1.8	400
fir, California red	Abies magnifica	2.2	500
fir, grand	Abies grandis	2.2	490
fir, noble	Abies procera	1.8	410
fir, pacific silver	Abies amabilis	1.9	430
fir, subalpine	Abies lasiocarpa	1.6	350
fir, white	Abies concolor	2.1	480
goncalo alves	Astronium graveolens	9.6	2160
greenheart	Chlorocardium rodiei	10.5	2350
hackberry	Celtis occidentalis	3.9	880
hackberry, netleaf	Celtis reticulata
(hackberry) sugarberry	Celtis laevigata
hemlock, eastern	Tsuga canadensis	2.2	500
hemlock, mountain	Tsuga mertensiana	3.0	680
hemlock, western	Tsuga heterophylla	2.4	540
hickory, bitternut	Carya cordiformis
hickory, black	Carya texana
hickory, nutmeg	Carya myristicaeformis
hickory, pecan	Carya illinoensis	8.1	1820
hickory, sand	Carya pallida
hickory, water	Carya aquatica
hickory. mockernut	Carya tomentosa
hickory, pignut	Carya glabra
hickory, shagbark	Carya ovata
hickory, shellbark	Carya lacinosa
holly, American	Ilex opaca	4.5	1020
honeylocust	Gleditsia triacanthos	7.0	1580
hophornbeam, eastern	Ostrya virginiana	8.3	1860
hornbeam, American	Carpinus caroliniana	7.9	1780
hura	Hura crepitans	2.4	550
ilomba	Pycnanthus angolensis	2.7	610
incense-cedar	Libocedrus decurrens	2.1	470
ipe	Tabebula spp., lapacho group	16.4	3680
iroko	Chlorophora spp.	5.6	1260
jarrah	Eucalyptus marginata	8.5	1910
jelutong	Dyera costulata	1.7 (@15%)	390
juniper, alligator	Juniperus deppeana	5.2	1160
juniper, western	Juniperus occidentalis
kaneelhart	Licaria spp.	12.9	2900
kapur	Dryobalanops spp.	5.5	1230
karri	Eucalyptus diversicolor	9.1	2040
kempas	Koompassia malaccensis	7.6	1710
keruing	Dipterocarpus spp.	5.6	1270
larch, western	Larix occidentalis	3.7	830
laurel, California	Umbellularia californica	5.6	1270
laurel, mountain	Kalmia latifolia	8.0	1790
lignumvitae	Guaiacum spp.	20.0	4500
limba	Terminalia superba	2.2	490
locust, black	Robinia pseudoacacia	7.6	1700
macawood	Platymiscium spp.	14.0??	3150
madrone, Pacific	Arbutus menziesii	6.5	1460
(magnolia) cucumber tree	Magnolia acuminata	3.1	700
magnolia, southern	Magnolia grandiflora	4.5	1020
(magnolia) sweetbay	Magnolia virginiana
mahogany, African	Khaya spp.	3.7	830
mahogany, true	Swietenia macrophylla	3.6	800
manbarklak	Eschweilera spp.	15.5	3480
manni	Symphonia globulifera	5.0	1120
maple, bigleaf	Acer macrophyllum	3.8	850
maple, black	Acer nigrum	5.2	1180
maple, red	Acer rubrum	4.2	950
maple, silver	Acer saccharimum	3.1	700
maple, sugar	Acer saccharum	6.4	1450
marishballi	Lincania spp.	15.9	3570
merbau	Intsia spp.	6.7  (@15%)	1500
mersawa	Anisoptera spp.	5.7	1290
mesquite	Prosopis spp.
mora	Mora spp.	10.2	2300
oak, black	Quercus velutina	5.4	1210
oak, cherrybark	Quercus falcata var pagodifolia	6.6	1480
oak, southern red	Quercus falcata	4.7	1060
oak, laurel	Quercus laurifolia	5.4	1210
oak, northern red	Quercus rubra	5.7	1290
oak, pin	Quercus palustris	6.7	1510
oak, scarlet	Quercus coccinea	6.2	1400
oak, shumard	Quercus shumardii
oak, water	Quercus nigra	5.3	1190
oak, willow	Quercus phellos	6.5	1460
oak, bur	Quercus macrocarpa	6.1	1370
oak, chestnut	Quercus prinus	5.0	1130
oak, live	Quercus virginiana
oak, overcup	Quercus lyrata	5.3	1190
oak, post	Quercus stellata	6.0	1360
oak, swamp chestnut	Quercus michauxii	5.5	1240
oak, swamp white	Quercus bicolor	7.2	1620
oak, white	Quercus alba	6.0	1360
obeche	Triplochiton scleroxylon	1.9	430
okoume	Aucoumea klaineana	1.7	380
opepe	Nauclea diderrichii	7.3	1630
osage orange	Maclura pomifera	9.1 (green)	2040 (green)
ovangkoi	Goubertia ehie
para-angelim	Hymenolobium excelsum	7.7	1720
parana-pine	Araucaria augustifolia	3.5	780
pau marfim	Balfourodendron riedelianum
peroba de campos	Paratecoma peroba	7.1	1600
peroba rosa	Aspidosperma spp., peroba group	7.7	1730
persimmon, common	Diospyros virginiana	10.2	2300
pilon	Hyeronima spp.	7.6	1700
pine, Caribbean	Pinus caribaea	5.5	1240
pine, eastern white	Pinus strobus	1.7	380
pine, jack	Pinus banksiana	2.5	570
pine, Jeffrey	Pinus jeffreyi	2.2	500
pine, limber	Pinus flexilis	1.9	430
pine, loblolly	Pinus taeda	3.1	690
pine, lodgepole	Pinus contorta	2.1	480
pine, longleaf	Pinus palustris	3.9	870
pine, ocote	Pinus oocarpa	4.0	910
pine, pinyon	Pinus edulis	3.8	860
pine, pitch	Pinus rigida	2.8	620
pine, pond	Pinus serotina	3.3	740
pine, ponderosa	Pinus ponderosa	2.0	460
pine, Monterey	Pinus radiata	3.3	750*
pine. red	Pinus resinosa	2.5	560
pine, sand	Pinus clausa	3.3	730
pine, shortleaf	Pinus echinata	3.1	690
pine, slash	Pinus elliotti
pine, spruce	Pinus glabra	2.9	660
pine, sugar	Pinus lambertiana	1.7	380
pine, Table Mountain	Pinus pungens	2.9	660
pine, virginia	Pinus virginiana	3.3	740
pine, western white	Pinus monticola	1.9	420
piquia	Caryocar spp.	7.7	1720
primavera	Tabebula donnell-smithii	2.9	660
purpleheart	Peltogyne spp.	8.3	1860
ramin	Gonystylus bancanus	5.8	1300
redcedar, eastern	Juniperus virginiana	4.0	900
redcedar, southern	Juniperus silicicola	2.7	610
redcedar, western	Thuja plicata	1.6	350
redwood, old growth	Sequoia sempervirens	2.1	480
redwood, second growth	Sequoia sempervirens	1.9	420
robe	Tabebul spp., roble group	4.3	960
rosewood, Brazilian	Dalbergia nigra	12.1	2720
rosewood, Indian	Dalbergia latifolia	14.1	3170
sande	Brosimum spp., utile group	4.0	900
santa maria	Calophyllum brasiliense	5.1	1150
sapele	Entandrophragma cylindricum	6.7	1510
sassafras	Sassafras albidum	2.8	630
sepetir	Pseudosindora palustris	6.3	1410
serviceberry	Amelanchier spp.	8.0	1800
shorea	Shorea spp., baulau group	7.9	1780
(shorea) dark red meranti	Shorea spp., lauan-meranti group	3.5	780
(shorea) light red meranti	Shorea spp., lauan-meranti group	2.0	460
(shorea) white meranti	Shorea spp., lauan-meranti group	5.1 (@15%)	1140
(shorea) yellow meranti	Shorea spp., lauan-meranti group	3.4	770
silverbell, Carolina	Halesia carolina	2.6	590
sourwood	Oxydendrum arboreum	4.2	940
Spanish-cedar	Cedrela spp.	2.7	600
spruce, black	Picea mariana	2.3	520
spruce, Engelmann	Picea engelmanni	1.7	390
spruce, red	Picea rubra	2.2	490
spruce, Sitka	Picea sitchensis	2.3	510
spruce, white	Picea glauca	2.1	480
sucupira	Bowdichia spp.
sucupira	Diplotropis purpurea	9.5	2140
sumac, staghorn	Rhus typhina	3.0	680
sweetgum	Liquidambar styraciflua	3.8	850
sycamore, american	Platanus occidentalis	3.4	770
tamarack	Larix laricina	2.6	590
tanoak	Lithocarpus densiflorus
teak	Tectona grandis	4.4	1000
tomillo	Cedrelinga catenformis		870 (green)
tree-of-heaven	Ailanthus altissima	7.7	1731
tupelo, black	Nyssa sylvatica	3.6	810
tupelo. water	Nyssa aquatica	3.9	880
wallaba	Eperua spp.	9.1	2040
walnut, black	Juglans nigra	4.5	1010
white-cedar, northern	Thuja occidentalis	1.4	320
willow, black	Salix nigra
witch hazel	Hamamelis virginica	6.8	1530
yellow poplar	Liriodendron tulipifera	2.4	540
yew. Pacific	Taxus brevifolia	7.1	1600