Black Locust wood movement, board-foot & weight calculator
- Janka
- 1,700lbf
- Density
- 48.2lb/ft³
- T/R ratio
- 1.6
- Spec. gravity
- 0.69
Black Locust is a North American hardwood. It has a Janka side hardness of 1,700 lbf, a specific gravity of 0.69, and an air-dry density near 48 lb/ft³ (772 kg/m³) (mechanical values at 12% moisture content). It shrinks 7.2% tangentially and 4.6% radially from green to oven-dry (T/R ratio 1.6), so a 12-inch flatsawn board moves about 0.17 in (≈ 3/16 in) across a 6-point moisture swing (about 6%→12% MC).
Compute Black Locust: movement, weight & board footage
Every number below is worked from Black Locust's own shrinkage and density figures, not looked up from a table — change the width, moisture swing, or board size in the calculators linked alongside.
Cross-grain movement by board width
| Board width | Flatsawn (tangential) | Quartersawn (radial) |
|---|---|---|
| 2″ | 0.029″ (≈ 1/32 in) | 0.018″ (≈ 1/32 in) |
| 3″ | 0.043″ (≈ 1/32 in) | 0.028″ (≈ 1/32 in) |
| 4″ | 0.058″ (≈ 1/16 in) | 0.037″ (≈ 1/32 in) |
| 6″ | 0.086″ (≈ 3/32 in) | 0.055″ (≈ 1/16 in) |
| 8″ | 0.115″ (≈ 1/8 in) | 0.074″ (≈ 1/16 in) |
| 10″ | 0.144″ (≈ 5/32 in) | 0.092″ (≈ 3/32 in) |
| 12″ | 0.173″ (≈ 3/16 in) | 0.11″ (≈ 1/8 in) |
| 16″ | 0.23″ (≈ 7/32 in) | 0.147″ (≈ 5/32 in) |
Need a different width or moisture swing? Run the movement calculator preloaded with Black Locust. At a T/R ratio of 1.57, Black Locust is stable — it moves moderately more across the face than through the thickness — normal behaviour for a furniture hardwood, and predictable if boards are acclimatised before milling.
Board footage & weight, standard sizes
| Nominal size × length | Board feet | Weight |
|---|---|---|
| 1×4 × 8′ | 2.67 bd ft | 10.7 lb |
| 1×6 × 8′ | 4 bd ft | 16.1 lb |
| 1×8 × 8′ | 5.33 bd ft | 21.4 lb |
| 1×10 × 8′ | 6.67 bd ft | 26.8 lb |
| 1×12 × 8′ | 8 bd ft | 32.1 lb |
| 2×4 × 8′ | 5.33 bd ft | 21.4 lb |
| 2×6 × 8′ | 8 bd ft | 32.1 lb |
| 2×8 × 8′ | 10.67 bd ft | 42.8 lb |
Different length or size? Run the board foot calculator or the weight calculator, both preloaded with Black Locust.
Seasonal movement by city
| City | Driest month (EMC) | Most-humid month (EMC) | EMC swing | 12″ board movement |
|---|---|---|---|---|
| Phoenix, AZ | Jun · 4.4% | Dec · 9% | 4.6 pts | 0.132″ (≈ 1/8 in) |
| Chicago, IL | May · 12.3% | Dec · 15.1% | 2.8 pts | 0.081″ (≈ 3/32 in) |
| Miami, FL | Apr · 12.2% | Sep · 14.4% | 2.2 pts | 0.063″ (≈ 1/16 in) |
| Boston, MA | Apr · 11.5% | Sep · 12.8% | 1.3 pts | 0.037″ (≈ 1/32 in) |
| Denver, CO | Jul · 8% | Dec · 10.5% | 2.5 pts | 0.072″ (≈ 1/16 in) |
| Seattle, WA | Jul · 12% | Dec · 16.9% | 4.9 pts | 0.141″ (≈ 5/32 in) |
Driven by Black Locust's tangential shrinkage of 7.2%. These are outdoor equilibrium-moisture figures, so they are an upper bound — a climate-controlled interior swings less. How this is calculated.
How Black Locust compares
Ranked against the 196 species in the Wood Handbook tables this site carries.
- Hardness: at 1,700 lbf, Black Locust is harder than 79% of the 157 species with a Janka figure.
- Weight: at 48.2 lb/ft³ it is heavier than 84% of the 170 species measured — an 8-foot 1×6 board weighs about 16.1 lb.
- Stability: its T/R ratio of 1.57 is more even than 78% of the 196 species here — as humidity changes, 22% of them hold their shape more evenly.
See Black Locust plotted against every species we carry: the full Janka hardness chart and the full density chart .
Species with a similar working profile
Closest matches on hardness, weight and stability together — useful when Black Locust is unavailable or priced out.
- Shagbark Hickory is a common substitute for Black Locust : 11% harder, about the same weight, and similarly stable in service.
- Jarrah is a common substitute for Black Locust : 12% harder, about the same weight, and similarly stable in service.
- Honeylocust is a common substitute for Black Locust : nearly identical hardness, 13% lighter, and similarly stable in service.
- Pecan Hickory is a common substitute for Black Locust : nearly identical hardness, about the same weight, and less stable in service.
| Species | Janka | Density | T/R |
|---|---|---|---|
| Shagbark Hickory | 1,880 lbf | 50.3 | 1.5 |
| Jarrah | 1,910 lbf | 46.8 | 1.43 |
| Honeylocust | 1,580 lbf | 41.9 | 1.57 |
| Pecan Hickory | 1,820 lbf | 46.1 | 1.82 |
About Black Locust
Black locust (Robinia pseudoacacia) is sometimes called yellow locust. This species grows from Pennsylvania along the Appalachian Mountains to northern Georgia and Alabama. It is also native to western Arkansas and southern Missouri. The greatest production of black locust timber is in Tennessee, Kentucky, West Virginia, and Virginia. It is attacked by an insect, the locust borer, whose larvae weaken trees by tunneling, making them susceptible to breakage by wind and ice. Repeated infestations lead to the loss of the timber’s value for use as fence posts or firewood. At present, however, the IUCN considers black locust to be a species of least concern. Locust has narrow, creamy white sapwood. The heartwood, when freshly cut, varies from greenish yellow to dark brown. Black locust is heavy, hard, resistant to shock, and strong and stiff. It has moderately low shrinkage. The heartwood has high decay resistance. Black locust is used for round, hewn, or split mine timbers as well as fence posts, poles, railroad crossties, stakes, and fuel. Other uses are for rough construction and crating. Historically, black locust was important for the manufacture of insulator pins and wooden pegs used in the construction of ships, for which the wood was well adapted because of its strength, decay resistance, and moderate shrinkage and swelling.
Durability & sustainability
Decay resistance: the Wood Handbook rates Black Locust heartwood very resistant to fungal decay . Ratings are for heartwood only and the table's own note cautions that resistance varies substantially within a species; treat this as a general indicator, not a guarantee, especially for ground contact. Wood Handbook, Chapter 14: Biodeterioration of Wood (Arango, Lebow, Glaeser), USDA Forest Products Laboratory, FPL-GTR-282 (2021), Table 14-1. Public domain.
CITES status: not listed on any CITES Appendix — no international-trade restriction applies to Black Locust.
Properties
| Specific gravity | 0.69 |
|---|---|
| Janka hardness (side) | 1,700 lbf |
| Density (air-dry, 12% MC) | 48.2 lb/ft³ (772 kg/m³) ovendry-weight basis: 43.1 lb/ft³ |
| Weight per board foot (air-dry) | 4.02 lb |
| Radial shrinkage (green→oven-dry) | 4.6% |
| Tangential shrinkage (green→oven-dry) | 7.2% |
| Volumetric shrinkage (green→oven-dry) | 10.2% |
| T/R ratio (stability indicator) | 1.6 |
Shrinkage is total green-to-oven-dry (Table 4-3); strength values are at 12% MC. Full bases and the derivation formulas are on the methodology page.
Data: USDA Forest Products Laboratory, Wood Handbook FPL-GTR-282 (2021), public domain.