Iroko wood movement, board-foot & weight calculator
- Janka
- 1,260lbf
- Density
- 37.7lb/ft³
- T/R ratio
- 1.4
- Spec. gravity
- 0.54
Iroko (Chlorophora excelsa and C. regia) is an imported species. It has a Janka side hardness of 1,260 lbf, a specific gravity of 0.54, and an air-dry density near 38 lb/ft³ (604 kg/m³) (mechanical values at 12% moisture content). It shrinks 3.8% tangentially and 2.8% radially from green to oven-dry (T/R ratio 1.4), so a 12-inch flatsawn board moves about 0.09 in (≈ 3/32 in) across a 6-point moisture swing (about 6%→12% MC).
Compute Iroko: movement, weight & board footage
Every number below is worked from Iroko'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″ | 0.015″ (≈ 0 in) | 0.011″ (≈ 0 in) |
| 3″ | 0.023″ (≈ 1/32 in) | 0.017″ (≈ 1/32 in) |
| 4″ | 0.03″ (≈ 1/32 in) | 0.022″ (≈ 1/32 in) |
| 6″ | 0.046″ (≈ 1/32 in) | 0.034″ (≈ 1/32 in) |
| 8″ | 0.061″ (≈ 1/16 in) | 0.045″ (≈ 1/32 in) |
| 10″ | 0.076″ (≈ 1/16 in) | 0.056″ (≈ 1/16 in) |
| 12″ | 0.091″ (≈ 3/32 in) | 0.067″ (≈ 1/16 in) |
| 16″ | 0.122″ (≈ 1/8 in) | 0.09″ (≈ 3/32 in) |
Need a different width or moisture swing? Run the movement calculator preloaded with Iroko. At a T/R ratio of 1.36, Iroko is very stable — it moves almost as much radially as tangentially, so flatsawn boards have little reason to cup and wide panels stay flat with ordinary care.
Board footage & weight, standard sizes
| Nominal size × length | Board feet | Weight |
|---|---|---|
| 1×4 × 8′ | 2.67 bd ft | 8.4 lb |
| 1×6 × 8′ | 4 bd ft | 12.6 lb |
| 1×8 × 8′ | 5.33 bd ft | 16.8 lb |
| 1×10 × 8′ | 6.67 bd ft | 20.9 lb |
| 1×12 × 8′ | 8 bd ft | 25.1 lb |
| 2×4 × 8′ | 5.33 bd ft | 16.8 lb |
| 2×6 × 8′ | 8 bd ft | 25.1 lb |
| 2×8 × 8′ | 10.67 bd ft | 33.5 lb |
Different length or size? Run the board foot calculator or the weight calculator, both preloaded with Iroko.
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 | 0.07″ (≈ 1/16 in) |
| Chicago, IL | May · 12.3% | Dec · 15.1% | 2.8 pts | 0.043″ (≈ 1/32 in) |
| Miami, FL | Apr · 12.2% | Sep · 14.4% | 2.2 pts | 0.033″ (≈ 1/32 in) |
| Boston, MA | Apr · 11.5% | Sep · 12.8% | 1.3 pts | 0.02″ (≈ 1/32 in) |
| Denver, CO | Jul · 8% | Dec · 10.5% | 2.5 pts | 0.038″ (≈ 1/32 in) |
| Seattle, WA | Jul · 12% | Dec · 16.9% | 4.9 pts | 0.074″ (≈ 1/16 in) |
Driven by Iroko's tangential shrinkage of 3.8%. These are outdoor equilibrium-moisture figures, so they are an upper bound — a climate-controlled interior swings less. How this is calculated.
How Iroko compares
Ranked against the 196 species in the Wood Handbook tables this site carries.
- Hardness: at 1,260 lbf, Iroko is harder than 64% of the 157 species with a Janka figure.
- Weight: at 37.7 lb/ft³ it is heavier than 52% of the 170 species measured — an 8-foot 1×6 board weighs about 12.6 lb.
- Stability: its T/R ratio of 1.36 is more even than 95% of the 196 species here — as humidity changes, 5% of them hold their shape more evenly.
See Iroko 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 Iroko is unavailable or priced out.
- Black Walnut is a common substitute for Iroko : 20% softer, about the same weight, and similarly stable in service.
- Yellow Birch is a common substitute for Iroko : nearly identical hardness, 15% heavier, and similarly stable in service.
- White Ash is a common substitute for Iroko : nearly identical hardness, 11% heavier, and less stable in service.
- Sapele is a common substitute for Iroko : 20% harder, about the same weight, and less stable in service.
| Species | Janka | Density | T/R |
|---|---|---|---|
| Black Walnut | 1,010 lbf | 38.4 | 1.42 |
| Yellow Birch | 1,260 lbf | 43.3 | 1.3 |
| White Ash | 1,320 lbf | 41.9 | 1.59 |
| Sapele | 1,510 lbf | 38.4 | 1.61 |
About Iroko
Iroko consists of two species (Milicia excelsa and M. regia). M. excelsa grows across the entire width of tropical Africa from the Ivory Coast southward to Angola and eastward to East Africa. M. regia, however, is limited to extreme West Africa from Gambia to Ghana; it is less resistant to drought than is M. excelsa. The heartwood varies from a pale yellowish brown to dark chocolate brown with light markings occurring most conspicuously on flat-sawn surfaces; the sapwood is yellowish white. The texture is medium to coarse, and the grain is typically interlocked. Iroko can be worked easily with hand or machine tools but with some tearing of interlocked grain. Occasional deposits of calcium carbonate severely damage cutting edges. The wood dries rapidly with little or no degrade. The strength is similar to that of red maple (Acer rubrum), and the weight is about 688 kg m–3 (43 lb ft–3) at 12% moisture content. The heartwood is very resistant to decay fungi and resistant to termite and marine borer attack. Because of its color and durability, iroko has been suggested as a substitute for teak (Tectona grandis). Its durability makes it suitable for boat building, piles, other marine work, and railroad crossties. Other uses include joinery, flooring, furniture, veneer, and cabinetwork.
Durability & sustainability
Decay resistance: the Wood Handbook rates Iroko heartwood 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.
Properties
| Specific gravity | 0.54 |
|---|---|
| Janka hardness (side) | 1,260 lbf |
| Density (air-dry, 12% MC) | 37.7 lb/ft³ (604 kg/m³) ovendry-weight basis: 33.7 lb/ft³ |
| Weight per board foot (air-dry) | 3.14 lb |
| Radial shrinkage (green→oven-dry) | 2.8% |
| Tangential shrinkage (green→oven-dry) | 3.8% |
| Volumetric shrinkage (green→oven-dry) | 8.8% |
| T/R ratio (stability indicator) | 1.4 |
Shrinkage is total green-to-oven-dry (Table 4-4); 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.