Wood species
Paper birch wood
Paper birch is a hardwood (Betula papyrifera). At 12% moisture content it has a Janka hardness of 910 lbf (4,048 N) and it weighs about 38 lb/ft³ (616 kg/m³), 3.2 lb (1.45 kg) per board foot.
Also called: Betula papyrifera.
Key numbers
- Janka hardness, 12% MC
- 910 lbf (4,048 N)
- Green: 560 lbf (2,491 N)
- Weight at 12% MC
- 38 lb/ft³ (616 kg/m³)
- 3.2 lb per board foot
- Specific gravity (oven-dry weight)
- 0.55 at 12% MC volume
- 0.48 on green volume
- Shrinkage, green to oven-dry
- 8.6% tangential
- Radial 6.3%, volumetric 16.2%
One source: USDA Forest Products Laboratory, the authority for species properties it measured
Why: Measured by the USDA Forest Products Laboratory; paper birch's density is worked from its specific gravity with the Handbook's own equation.
How much paper birch moves
A 12 in wide flatsawn board of paper birch 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 0.16 in (about 5/32 in, 4 mm). Flatsawn faces move 1.4 times as much as quartersawn ones, because the wood shrinks 8.6% around the growth rings but only 6.3% across them.
Worked with the Wood Handbook's dimensional change coefficients for paper birch (Table 13-5: 0.00304 tangential, 0.00219 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
- The Handbook gives no separate color for paper birch.
- Working and character
- Lighter, softer and weaker than yellow and sweet birch. Birch shrinks considerably as it dries.
- Uses
- Toothpicks, tongue depressors, ice cream sticks, and turned goods such as spools, bobbins, small handles and toys.
Paper birch grows right across the continent.
Adapted in our own words from the Wood Handbook, Chapter 2, p. 2-5.
Strength
Bending strength is the modulus of rupture (MOR); stiffness is the modulus of elasticity (MOE). Clear, straight-grained samples of paper birch 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) | 6,400 psi (44 MPa) | 12,300 psi (85 MPa) |
| Stiffness (MOE) | 1,170,000 psi (8.1 GPa) | 1,590,000 psi (11 GPa) |
| Crushing strength (compression parallel to grain) | 2,360 psi (16 MPa) | 5,690 psi (39 MPa) |
| Compression perpendicular to grain | 270 psi (2 MPa) | 600 psi (4 MPa) |
| Shear parallel to grain | 840 psi (6 MPa) | 1,210 psi (8 MPa) |
| Tension perpendicular to grain | 380 psi (3 MPa) | — |
A dash means the Handbook prints no value; none is filled in.
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
Buying and finishing paper birch
Work it out for your project
- Rank woods for turning with the species picker
Weigh paper birch against other woods on hardness, weight, movement and color, every figure from the Wood Handbook.
Why these numbers
Why these numbers?
The situation
The USDA Forest Products Laboratory measured paper birch at 910 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 × 0.55 × 1.12.
Arithmetic: exact by definition , sources [1]
The number
About 38 lb/ft³, or 3.2 lb per board foot (1/12 ft³), at 12% moisture content.
Arithmetic: exact by definition
Sources