Species data
Black Locust
Robinia pseudoacacia - a hardwood from central and eastern United States. Also sold as robinia, false acacia.
Properties at a glance
| Janka hardness | 1,700 lbf |
| Stiffness (MOE) | 2,050,000 psi |
| Specific gravity | 0.77 |
| Density | 48.0 lb/ft3 (770 kg/m3) |
| Weight per board foot | 4.00 lb |
| Shrinkage, green to oven-dry | 7.2% tangential / 4.6% radial |
| Indicative price | $6.00 per board foot (estimated) |
Values are at about 12% moisture content. Density is specific gravity times 62.4; a board foot is one twelfth of a cubic foot, so weight per board foot is that density divided by twelve. Anything marked estimated is our own figure, not a measured one.
How Black Locust compares
Measured against the 113 solid woods in this database: it is harder than 73% of them, heavier than 73%, and stiffer than 81%.
What that means in the shop
A 4/4 board 8 inches wide and 8 feet long is 5.33 board feet, so in Black Locust it weighs about 21.4 lb. A stack of ten is 214 lb - worth knowing before you load a rack or a car.
Against red oak, the trade's usual yardstick at 1,220 lbf, Black Locust is about 1.4x as hard and 1.10x as heavy.
Its shrinkage is 7.2% tangential against 4.6% radial, a ratio of 1.6 to 1. The wider that ratio, the more unevenly a flatsawn board moves across its width as humidity changes, and the more it wants to cup; anything near or above 2 to 1 is worth quartersawing or restraining for panels and wide tops. This one moves comparatively evenly.
Woods of similar hardness
Closest to Black Locust on hardness in this database: African Padauk (1,710 lbf), Garapa (1,650 lbf), European Hornbeam (1,630 lbf), American Hornbeam (1,780 lbf). Similar hardness does not mean similar behaviour - check density and movement before substituting one for another.
Working with it
Workability. Dense and hard, machining proves tough and edges dull moderately; steam-bends and turns superbly; finishes and glues well
Durability. Very durable and weathers well; long favored for fence posts left outdoors
Typical uses. fence posts, flooring, furniture, boatbuilding, turned objects, veneer.
Related calculators
Sources
MOE, SG (12% MC), Janka and shrinkage from The Wood Database (cites USDA FPL Wood Handbook). Uses, region, durability and workability summarized from The Wood Database. Black Locust is not listed in the FPL/Hoadley dimensional change coefficient table (Popular Woodworking reproduction), so CT/CR are omitted. Price indicative.
These calculators are for planning and estimation. Engineering results (shelf sag, wood movement) use published average material properties; real boards vary by grade, grain, moisture and defects. Verify load-bearing designs with a professional.