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Black locust

Robinia pseudoacacia

U.S. hardwood · United States

Black locust measures 1,700 lbf on the Janka scale, 32% harder than northern red oak.

  • Its bending strength is 49% above the median for U.S. hardwoods.
  • Drying barely changes its hardness: from 1,570 lbf green, it gains only 8% by 12% moisture, against a median of 31%.
  • Pilon has exactly the same Janka figure.
  • Across all 155 woods it falls in the top fifth for hardness, density and bending strength and in the bottom fifth for volumetric shrinkage.

Compare black locust

U.S. hardwoodsU.S. softwoodsImported woodsNorthern red oak

Black locust · 1,700 lbfCeibaEastern white pineBlack cherryShagbark hickoryIpe01,0002,0003,0004,000 lbf← softerharder →Ceiba, 240 lbfNorthern white-cedar, 320 lbfAtlantic white-cedar, 350 lbfBlack cottonwood, 350 lbfQuaking aspen, 350 lbfSubalpine fir, 350 lbfWestern redcedar, 350 lbfBalsam fir, 380 lbfCuangare, 380 lbfEastern white pine, 380 lbfOkoume, 380 lbfSugar pine, 380 lbfEngelmann spruce, 390 lbfAmerican basswood, 410 lbfNoble fir, 410 lbfRedwood (young-growth), 420 lbfWestern white pine, 420 lbfEastern cottonwood, 430 lbfObeche, 430 lbfPacific silver fir, 430 lbfLight red meranti, 460 lbfPonderosa pine, 460 lbfIncense-cedar, 470 lbfLodgepole pine, 480 lbfRedwood (old-growth), 480 lbfWhite fir, 480 lbfButternut, 490 lbfGrand fir, 490 lbfLimba, 490 lbfCalifornia red fir, 500 lbfEastern hemlock, 500 lbfBanak, 510 lbfSitka spruce, 510 lbfBlack spruce, 530 lbfAmerican chestnut, 540 lbfWestern hemlock, 540 lbfYellow-poplar, 540 lbfHura, 550 lbfRed pine, 560 lbfJack pine, 570 lbfYellow-cedar, 580 lbfRed alder, 590 lbfTamarack, 590 lbfDouglas-fir (Interior North), 600 lbfSpanish-cedar, 600 lbfIlomba, 610 lbfCativo, 630 lbfPort-Orford-cedar, 630 lbfDeterma, 660 lbfDouglas-fir (Interior West), 660 lbfPrimavera, 660 lbfMountain hemlock, 680 lbfLoblolly pine, 690 lbfShortleaf pine, 690 lbfCucumbertree, 700 lbfSilver maple, 700 lbfDouglas-fir (Coast), 710 lbfVirginia pine, 740 lbfAmerican sycamore, 770 lbfYellow meranti, 770 lbfDark red meranti, 780 lbfParana-pine, 780 lbfMahogany, 800 lbfBlack tupelo, 810 lbfAfrican mahogany, 830 lbfAmerican elm, 830 lbfWestern larch, 830 lbfBigleaf maple, 850 lbfBlack ash, 850 lbfSweetgum, 850 lbfSlippery elm, 860 lbfLongleaf pine, 870 lbfHackberry, 880 lbfWater tupelo, 880 lbfSande, 900 lbfOcote pine, 910 lbfPaper birch, 910 lbfBlack cherry, 950 lbfRed maple, 950 lbfRoble, 960 lbfTeak, 1,000 lbfBlack walnut, 1,010 lbfAlbarco, 1,020 lbfSouthern magnolia, 1,020 lbfSouthern red oak, 1,060 lbfAvodire, 1,080 lbfManni, 1,120 lbfAndiroba, 1,130 lbfChestnut oak, 1,130 lbfOregon ash, 1,160 lbfBlack maple, 1,180 lbfOvercup oak, 1,190 lbfWater oak, 1,190 lbfGreen ash, 1,200 lbfBlack oak, 1,210 lbfLaurel oak, 1,210 lbfKapur, 1,230 lbfCaribbean pine, 1,240 lbfSwamp chestnut oak, 1,240 lbfIroko, 1,260 lbfYellow birch, 1,260 lbfKeruing, 1,270 lbfAngelique, 1,290 lbfMersawa, 1,290 lbfNorthern red oak, 1,290 lbfAmerican beech, 1,300 lbfRamin, 1,300 lbfRock elm, 1,320 lbfWhite ash, 1,320 lbfPost oak, 1,360 lbfWhite oak, 1,360 lbfBur oak, 1,370 lbfScarlet oak, 1,400 lbfSepetir, 1,410 lbfSugar maple, 1,450 lbfWillow oak, 1,460 lbfSweet birch, 1,470 lbfPin oak, 1,510 lbfSapele, 1,510 lbfAfrormosia, 1,560 lbfHoneylocust, 1,580 lbfPeroba de campos, 1,600 lbfOpepe, 1,630 lbfPilon, 1,700 lbfKempas, 1,710 lbfPara-angelim, 1,720 lbfPiquia, 1,720 lbfPeroba rosa, 1,730 lbfAngelin, 1,750 lbfBenge, 1,750 lbfShellbark hickory, 1,810 lbfPurpleheart, 1,860 lbfShagbark hickory, 1,880 lbfJarrah, 1,910 lbfDegame, 1,940 lbfMockernut hickory, 1,970 lbfKarri, 2,040 lbfPignut hickory, 2,140 lbfSucupira, 2,140 lbfGoncalo alves, 2,160 lbfMora, 2,300 lbfCourbaril, 2,350 lbfGreenheart, 2,350 lbfTropical oak (roble), 2,500 lbfBubinga, 2,690 lbfBrazilian rosewood, 2,720 lbfKaneelhart, 2,900 lbfMacawood, 3,150 lbfIndian rosewood, 3,170 lbfBulletwood, 3,190 lbfAzobe, 3,350 lbfManbarklak, 3,480 lbfMarishballi, 3,570 lbfIpe, 3,680 lbfBlack locust · 1,700 lbfIpe01,0002,0003,0004,000 lbf← softerharder →

Six measures

Black locustU.S. hardwoods medianOther woods

  • Bending strength

    19,400 psi133.8 MPa19th strongest of 155
    4,300 psi29,900 psi
    49% above the U.S. hardwoods median

  • Density

    0.660.69 at 12% MC25th heaviest of 155
    0.250.96
    27% above the U.S. hardwoods median

  • Janka hardness

    1,700 lbf7,562 N31st hardest of 155
    240 lbf3,680 lbf
    5th of 53 U.S. hardwoods; 47% above the U.S. hardwoods median

  • Stiffness

    2.05 M psi14.1 GPa34th stiffest of 155
    0.54 M psi4.06 M psi
    28% above the U.S. hardwoods median

  • Cupping tendency

    1.5735th lowest of 155
    1.092.90

  • Shrinkage across the face

    7.2%radial 4.6%54th lowest of 155
    3.5%12.7%

For its weight: strength-to-weight 29,394 psi (19th of 155).

How much it moves

The two directions move almost alike (T/R 1.57), so flatsawn and quartersawn boards differ by only 0.16 in.

0.43 in.

off a 6-inch flatsawn board, green to oven-dry

Tangential
7.2%
Radial
4.6%
Volume
10.2%
T/R ratio
1.57 (35th most stable of 155)
6 in. green (dashed)5.57 in. dry · −7.2%
Flatsawn
6 in. green (dashed)5.72 in. dry · −4.6%
Quartersawn

End view, shrinkage drawn 3× life size.

Closest substitutes

  • Para-angelim

    1% harder · 4% lighter · shrinks 0.1 points less across the face

  • Opepe

    4% softer · 4% lighter · shrinks 1.2 points more across the face

  • Piquia

    1% harder · 9% heavier · shrinks 0.8 points more across the face

Compare with the first two

Woods of similar hardness

The eight nearest on the Janka scale, lbf.

Laboratory values

Its most unusual laboratory figure is crushing strength across the grain: 3rd highest of the 90 woods with a published value.

PropertyGreenDry, 12% MCChange when driedMetric, 12% MC
Compression perpendicular1,160psi1,830psi+58%12.6MPa
Shear parallel to grain1,760psi2,480psi+41%17.1MPa
Impact bending44in.57in.+30%1,448mm
Compression parallel to grain6,800psi10,180psi+50%70.2MPa
Modulus of rupture13,800psi19,400psi+41%133.8MPa
Work to maximum load15.4in-lbf/in³18.4in-lbf/in³+19%126.9kJ/m³
Side hardness1,570lbf1,700lbf+8%7,562N
Modulus of elasticity1.85M psi2.05M psi+11%14.1GPa
Tension perpendicular770psi640psi−17%4.40MPa

Wood Handbook Table 5-3b, Table 4-3. Data & method · Guides