Wood species
Spruce wood
Spruce is a softwood; this page covers the eastern spruces and engelmann spruce, led by red spruce (Picea rubens). At 12% moisture content it has a Janka hardness of 530 lbf (2,358 N) and it weighs about 28 lb/ft³ (448 kg/m³), 2.3 lb (1.06 kg) per board foot.
Names and species on this page: eastern spruce, red spruce, white spruce, black spruce, Engelmann spruce, mountain spruce.
Key numbers
- Janka hardness, 12% MC
- 530 lbf (2,358 N)
- Green: 340 lbf (1,512 N)
- Weight at 12% MC
- 28 lb/ft³ (448 kg/m³)
- 2.3 lb per board foot
- Specific gravity (oven-dry weight)
- 0.40 at 12% MC volume
- 0.37 on green volume
- Shrinkage, green to oven-dry
- 7.8% tangential
- Radial 3.8%, volumetric 11.8%
One source: USDA Forest Products Laboratory, the authority for species properties it measured
Why: Measured by the USDA Forest Products Laboratory; spruce's density is worked from its specific gravity with the Handbook's own equation.
How much spruce moves
A 12 in wide flatsawn board of red spruce that goes from 6% to 12% moisture content swells about 0.2 in (about 3/16 in, 5 mm). Quartersawn, the same board moves about 0.09 in (about 3/32 in, 2.4 mm). Flatsawn faces move 2.1 times as much as quartersawn ones, because the wood shrinks 7.8% around the growth rings but only 3.8% across them.
Worked with the Wood Handbook's dimensional change coefficients for red spruce (Table 13-5: 0.00274 tangential, 0.0013 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
- Light colored, with little difference between heartwood and sapwood; Engelmann spruce is nearly white with a slight red tinge.
- Grain and texture
- Medium to fine texture; Engelmann spruce lumber usually carries many small knots.
- Working and character
- The eastern spruces are moderately light, easily worked, moderately strong and stiff, with moderate shrinkage, and dry easily. Engelmann spruce is lighter, softer and weaker.
- Uses
- Framing lumber, millwork, boxes and crates, and piano soundboards; much of it goes to pulp.
Adapted in our own words from the Wood Handbook, Chapter 2, p. 2-17 to 2-18.
Strength
Bending strength is the modulus of rupture (MOR); stiffness is the modulus of elasticity (MOE). Clear, straight-grained samples of red spruce 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) | 6,000 psi (41 MPa) | 10,800 psi (74 MPa) |
| Stiffness (MOE) | 1,330,000 psi (9.2 GPa) | 1,660,000 psi (11.4 GPa) |
| Crushing strength (compression parallel to grain) | 2,720 psi (19 MPa) | 5,540 psi (38 MPa) |
| Compression perpendicular to grain | 260 psi (2 MPa) | 550 psi (4 MPa) |
| Shear parallel to grain | 750 psi (5 MPa) | 1,290 psi (9 MPa) |
| Tension perpendicular to grain | 220 psi (2 MPa) | 350 psi (2 MPa) |
A dash means the Handbook prints no value; none is filled in.
The eastern spruces and engelmann spruce
The Handbook tests each species separately; they are sold together as spruce. Across the 4 species measured, Janka hardness at 12% runs from 390 to 530 lbf.
| Species | Janka, 12% MC | Weight, 12% MC | Tangential shrinkage |
|---|---|---|---|
| Red sprucePicea rubens | 530 lbf | 28 lb/ft³ | 7.8% |
| White sprucePicea glauca | 410 lbf | 25 lb/ft³ | — |
| Black sprucePicea mariana | 530 lbf | 29 lb/ft³ | 6.8% |
| Engelmann sprucePicea engelmannii | 390 lbf | 24 lb/ft³ | 7.1% |
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 red spruce at 530 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 × 0.40 × 1.12.
Arithmetic: exact by definition , sources [1]
The number
About 28 lb/ft³, or 2.3 lb per board foot (1/12 ft³), at 12% moisture content.
Arithmetic: exact by definition
Sources