Black Locust
Robinia pseudoacacia · hardwood · Eastern North America · moderate movement
- Janka hardness 1,700 lbfred oak ≈ 1,290 lbf
- Density ≈ 48 lb/ft³specific gravity 0.69 at 12% MC
- Shrinkage — tangential 7.2%flatsawn width, green → ovendry
- Shrinkage — radial 4.6%quartersawn width
- T/R ratio 1.6 : 1higher = more cupping in flatsawn stock
Shop notes Extremely rot-resistant — the domestic answer to tropical decking. Hard on tools, glows yellow-green under UV, and holds fasteners ferociously.
Seasonal movement at a glance
Width change for black locust across a typical indoor year — 6% moisture content in the heated winter to 12% in a humid summer:
| Board width | Flatsawn | Quartersawn |
|---|---|---|
| 6″ | 3/32″ (0.093″) | 1/16″ (0.059″) |
| 12″ | 3/16″ (0.185″) | 1/8″ (0.118″) |
| 24″ | 3/8″ (0.370″) | 1/4″ (0.237″) |
| 36″ | 9/16″ (0.555″) | 11/32″ (0.355″) |
Run your own numbers
Different width, different climate swing — the calculator below is preset to black locust:
Typical swings:
Black Locust questions
How much does black locust move with the seasons?
A 12″-wide flatsawn black locust board moves about 3/16″ across a typical indoor swing from 6% to 12% moisture content; quartersawn, about 1/8″. Its tangential shrinkage is 7.2% and radial 4.6% (green to ovendry) — a moderate-movement wood.
How hard is black locust?
Black Locust rates about 1,700 lbf on the Janka scale — noticeably harder than red oak (red oak is roughly 1,290 lbf). Density runs about 48 lb/ft³ at indoor moisture levels.
Is black locust good for wide panels and tabletops?
Yes, with normal precautions: its 1.6:1 tangential-to-radial ratio is unusually balanced, so panels stay flatter than most. Still fasten solid tops so they can move across their width.
Similar species
Pecan (Hickory) · Honeylocust · Afrormosia · Shagbark Hickory · Pin Oak · Sweet Birch
Shrinkage, specific gravity, and hardness from the Wood Handbook, FPL-GTR-282 (2021 edition), USDA Forest Products Laboratory (public domain). Values are species averages — individual boards vary with growth conditions and how they were dried.