Coast Douglas-fir — wood data
- Janka
- 710lbf
- Density
- 33.5lb/ft³
- T/R ratio
- 1.6
- Spec. gravity
- 0.48
Coast Douglas-fir is a North American softwood. It has a Janka side hardness of 710 lbf, a specific gravity of 0.48, and an air-dry density near 34 lb/ft³ (537 kg/m³) (mechanical values at 12% moisture content). It shrinks 7.6% tangentially and 4.8% radially from green to oven-dry (T/R ratio 1.6), so a 12-inch flatsawn board moves about 0.18 in (≈ 3/16 in) across a 6-point moisture swing (about 6%→12% MC).
Properties
| Specific gravity | 0.48 |
|---|---|
| Janka hardness (side) | 710 lbf |
| Density (air-dry, 12% MC) | 33.5 lb/ft³ (537 kg/m³) ovendry-weight basis: 30 lb/ft³ |
| Weight per board foot (air-dry) | 2.79 lb |
| Radial shrinkage (green→oven-dry) | 4.8% |
| Tangential shrinkage (green→oven-dry) | 7.6% |
| Volumetric shrinkage (green→oven-dry) | 12.4% |
| T/R ratio (stability indicator) | 1.6 |
Shrinkage is total green-to-oven-dry (Table 4-3). Specific gravity basis: ovendry weight, volume at 12% MC. Janka side hardness at 12% MC. Primary density is air-dry at 12% MC: 62.4 × specific gravity × 1.12 (includes the ~12% bound-water mass — how dried lumber is actually weighed). The ovendry-weight figure (62.4 × SG, wood substance only) is shown beneath it.
Data: USDA Forest Products Laboratory, Wood Handbook FPL-GTR-282 (2021), public domain.
Estimated movement by board width
| Board width | Flatsawn (tangential) | Quartersawn (radial) |
|---|---|---|
| 4″ | 0.061″ (≈ 1/16 in) | 0.038″ (≈ 1/32 in) |
| 6″ | 0.091″ (≈ 3/32 in) | 0.058″ (≈ 1/16 in) |
| 8″ | 0.122″ (≈ 1/8 in) | 0.077″ (≈ 1/16 in) |
| 12″ | 0.182″ (≈ 3/16 in) | 0.115″ (≈ 1/8 in) |
Need a different width or moisture swing? Run the movement calculator preloaded with Coast Douglas-fir. A T/R ratio near 1 means the wood moves evenly in both directions and tends to stay flat; higher ratios cup and distort more as moisture changes.
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 | 0.14″ (≈ 1/8 in) |
| Chicago, IL | May · 12.3% | Dec · 15.1% | 2.8 pts | 0.085″ (≈ 3/32 in) |
| Miami, FL | Apr · 12.2% | Sep · 14.4% | 2.2 pts | 0.067″ (≈ 1/16 in) |
Computed with ΔD = D × (S ÷ 30 ÷ 100) × ΔEMC, where S is Coast Douglas-fir's total green-to-oven-dry tangential shrinkage (7.6%) and 30% is the fiber-saturation-point convention. The EMC figures are USDA Table 13-1 monthly equilibrium moisture content for outdoor exposure (through 2010); a climate-controlled interior swings less, so treat these as an upper-bound seasonal range for each location.
Sources & method
Shrinkage, specific gravity, and hardness values follow the USDA Forest Products Laboratory Wood Handbook (FPL-GTR-282, 2021); derived figures (movement, weight per board foot, T/R ratio, kg/m³, density from specific gravity) are computed with the formulas documented on the methodology page.