Wood species
Douglas-fir wood
Douglas-fir is a softwood; this page covers the douglas-fir (coast and interior), led by coast Douglas-fir (Pseudotsuga menziesii). At 12% moisture content it has a Janka hardness of 710 lbf (3,158 N) and it weighs about 34 lb/ft³ (538 kg/m³), 2.8 lb (1.27 kg) per board foot.
Names and species on this page: Douglas fir, red-fir, yellow-fir, Douglas-spruce.
Key numbers
- Janka hardness, 12% MC
- 710 lbf (3,158 N)
- Green: 500 lbf (2,224 N)
- Weight at 12% MC
- 34 lb/ft³ (538 kg/m³)
- 2.8 lb per board foot
- Specific gravity (oven-dry weight)
- 0.48 at 12% MC volume
- 0.45 on green volume
- Shrinkage, green to oven-dry
- 7.6% tangential
- Radial 4.8%, volumetric 12.4%
One source: USDA Forest Products Laboratory, the authority for species properties it measured
Why: Measured by the USDA Forest Products Laboratory; Douglas-fir's density is worked from its specific gravity with the Handbook's own equation.
How much Douglas-fir moves
A 12 in wide flatsawn board of coast Douglas-fir that goes from 6% to 12% moisture content swells about 0.19 in (about 3/16 in, 4.9 mm). Quartersawn, the same board moves about 0.12 in (about 1/8 in, 3 mm). Flatsawn faces move 1.6 times as much as quartersawn ones, because the wood shrinks 7.6% around the growth rings but only 4.8% across them.
Worked with the Wood Handbook's dimensional change coefficients for coast Douglas-fir (Table 13-5: 0.00267 tangential, 0.00165 radial per 1% change in moisture content), which hold between 6% and 14%. Individual boards vary: the Handbook gives shrinkage a coefficient of variation of about 15% (p. 4-11).
Color, grain and working
- Color
- Reddish heartwood in young, fast-grown trees (“red-fir”); yellowish brown in narrow-ringed old growth (“yellow-fir”).
- Working and character
- Varies widely in weight and strength; the Handbook advises the denser wood where strength matters.
- Uses
- Building lumber, beams, plywood, millwork, doors and sashes; some flooring, furniture and boats.
Adapted in our own words from the Wood Handbook, Chapter 2, p. 2-11 to 2-12.
Strength
Bending strength is the modulus of rupture (MOR); stiffness is the modulus of elasticity (MOE). Clear, straight-grained samples of coast Douglas-fir tested by the Forest Products Laboratory (Wood Handbook Table 5-3b). Knots and cross grain make lumber weaker than these clear samples (Handbook Chapter 5).
| Property | Green | 12% MC |
|---|---|---|
| Bending strength (MOR) | 7,700 psi (53 MPa) | 12,400 psi (85 MPa) |
| Stiffness (MOE) | 1,560,000 psi (10.8 GPa) | 1,950,000 psi (13.4 GPa) |
| Crushing strength (compression parallel to grain) | 3,780 psi (26 MPa) | 7,230 psi (50 MPa) |
| Compression perpendicular to grain | 380 psi (3 MPa) | 800 psi (6 MPa) |
| Shear parallel to grain | 900 psi (6 MPa) | 1,130 psi (8 MPa) |
| Tension perpendicular to grain | 300 psi (2 MPa) | 340 psi (2 MPa) |
A dash means the Handbook prints no value; none is filled in.
The douglas-fir (coast and interior)
The Handbook tests each species separately; they are sold together as Douglas-fir. Across the 4 species measured, Janka hardness at 12% runs from 510 to 710 lbf.
| Species | Janka, 12% MC | Weight, 12% MC | Tangential shrinkage |
|---|---|---|---|
| Coast Douglas-firPseudotsuga menziesii | 710 lbf | 34 lb/ft³ | 7.6% |
| Interior west Douglas-firPseudotsuga menziesii | 660 lbf | 35 lb/ft³ | 7.5% |
| Interior north Douglas-firPseudotsuga menziesii | 600 lbf | 34 lb/ft³ | 6.9% |
| Interior south Douglas-firPseudotsuga menziesii | 510 lbf | 32 lb/ft³ | — |
Dust and health
- Wood dust is classed as carcinogenic to humans (Group 1) by the International Agency for Research on Cancer, chiefly for cancers of the nose and sinuses.
- NIOSH recommends keeping wood dust exposure to 1 mg/m³ of total dust, as quoted in OSHA's sawmill guidance.
This is what the named authorities publish, not medical advice.
Compare with
Why these numbers
Why these numbers?
The situation
The USDA Forest Products Laboratory measured coast Douglas-fir at 710 lbf of side hardness at 12% moisture content, on clear, straight-grained samples (Wood Handbook Table 5-3b).
One source: USDA Forest Products Laboratory, the authority for species properties it measured , sources [1]
What that means
Side hardness (Janka) is the load needed to press a 0.444 in (11.28 mm) steel ball halfway into the wood across the grain; a higher number dents less (Handbook p. 5-5).
One source: USDA Forest Products Laboratory, the authority for species properties it measured , sources [1]
So
Density at 12% is water's density × specific gravity × (1 + 0.12) (Handbook Eq. 4-14): 62.43 × 0.48 × 1.12.
Arithmetic: exact by definition , sources [1]
The number
About 34 lb/ft³, or 2.8 lb per board foot (1/12 ft³), at 12% moisture content.
Arithmetic: exact by definition
Sources