Wood species
Red oak wood
Red oak is a hardwood; this page covers the red oak group, led by northern red oak (Quercus rubra). At 12% moisture content it has a Janka hardness of 1,290 lbf (5,738 N) and it weighs about 44 lb/ft³ (706 kg/m³), 3.7 lb (1.67 kg) per board foot.
Names and species on this page: northern red oak, black oak, cherrybark oak, pin oak, scarlet oak, southern red oak, water oak, willow oak.
Key numbers
- Janka hardness, 12% MC
- 1,290 lbf (5,738 N)
- Green: 1,000 lbf (4,448 N)
- Weight at 12% MC
- 44 lb/ft³ (706 kg/m³)
- 3.7 lb per board foot
- Specific gravity (oven-dry weight)
- 0.63 at 12% MC volume
- 0.56 on green volume
- Shrinkage, green to oven-dry
- 8.6% tangential
- Radial 4.0%, volumetric 13.7%
One source: USDA Forest Products Laboratory, the authority for species properties it measured
Why: Measured by the USDA Forest Products Laboratory; red oak's density is worked from its specific gravity with the Handbook's own equation.
How much red oak moves
A 12 in wide flatsawn board of northern red oak that goes from 6% to 12% moisture content swells about 0.22 in (about 7/32 in, 5.6 mm). Quartersawn, the same board moves about 0.1 in (about 3/32 in, 2.5 mm). Flatsawn faces move 2.2 times as much as quartersawn ones, because the wood shrinks 8.6% around the growth rings but only 4.0% across them.
Worked with the Wood Handbook's dimensional change coefficients for northern red oak (Table 13-5: 0.00304 tangential, 0.00137 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
- Brown heartwood with a tinge of red; nearly white sapwood 1 to 2 in. wide.
- Grain and texture
- Open pores (red oak generally lacks the tyloses that plug white oak’s), and broad, conspicuous rays on quartersawn faces. The species can’t be told apart as lumber.
- Working and character
- Heavy, with fairly high shrinkage while drying. Fast-grown second growth is generally harder and tougher than fine-textured old growth.
- Uses
- Flooring, furniture, millwork, cabinets, boxes, pallets, handles and veneer. Its open pores make it unsuitable for tight barrels unless lined.
Adapted in our own words from the Wood Handbook, Chapter 2, p. 2-9.
Strength
Bending strength is the modulus of rupture (MOR); stiffness is the modulus of elasticity (MOE). Clear, straight-grained samples of northern red oak 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) | 8,300 psi (57 MPa) | 14,300 psi (99 MPa) |
| Stiffness (MOE) | 1,350,000 psi (9.3 GPa) | 1,820,000 psi (12.5 GPa) |
| Crushing strength (compression parallel to grain) | 3,440 psi (24 MPa) | 6,760 psi (47 MPa) |
| Compression perpendicular to grain | 610 psi (4 MPa) | 1,010 psi (7 MPa) |
| Shear parallel to grain | 1,210 psi (8 MPa) | 1,780 psi (12 MPa) |
| Tension perpendicular to grain | 750 psi (5 MPa) | 800 psi (6 MPa) |
A dash means the Handbook prints no value; none is filled in.
The red oak group
The Handbook tests each species separately; they are sold together as red oak. Across the 9 species measured, Janka hardness at 12% runs from 1,060 to 1,510 lbf.
| Species | Janka, 12% MC | Weight, 12% MC | Tangential shrinkage |
|---|---|---|---|
| Northern red oakQuercus rubra | 1,290 lbf | 44 lb/ft³ | 8.6% |
| Black oakQuercus velutina | 1,210 lbf | 43 lb/ft³ | 11.1% |
| Cherrybark oakQuercus falcata var. pagodaefolia | 1,480 lbf | 48 lb/ft³ | — |
| Laurel oakQuercus laurifolia | 1,210 lbf | 44 lb/ft³ | 9.9% |
| Pin oakQuercus palustris | 1,510 lbf | 44 lb/ft³ | 9.5% |
| Scarlet oakQuercus coccinea | 1,400 lbf | 47 lb/ft³ | 10.8% |
| Southern red oakQuercus falcata | 1,060 lbf | 41 lb/ft³ | 11.3% |
| Water oakQuercus nigra | 1,190 lbf | 44 lb/ft³ | 9.8% |
| Willow oakQuercus phellos | 1,460 lbf | 48 lb/ft³ | 9.6% |
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 northern red oak at 1,290 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 × 0.63 × 1.12.
Arithmetic: exact by definition , sources [1]
The number
About 44 lb/ft³, or 3.7 lb per board foot (1/12 ft³), at 12% moisture content.
Arithmetic: exact by definition
Sources