Lumber and Wood Species Properties

Wood is one of the most variable structural materials in common use. The same species can differ by 20 to 30% in strength depending on moisture content, growth rate and grain orientation, which is why lumber grading exists at all. Knowing the key properties is what lets you pick the right species for a job.

Janka Hardness measures the force (in pounds-force, lbf) required to embed a 0.444-inch (11.28 mm) steel ball to half its diameter into the wood. It is the most widely used measure of wear resistance and hardness for flooring and woodworking applications. Higher Janka = harder, more scratch-resistant, and usually harder to work with hand tools.

Modulus of Elasticity (MOE), measured in million psi (Mpsi), is stiffness. Higher MOE means less deflection under load, which is what matters for beams, floor joists and shelving. Douglas Fir at 1.95 Mpsi sags noticeably less than Ponderosa Pine at 1.29 under the same load, and that is most of why Fir dominates structural framing.

Modulus of Rupture (MOR), measured in psi, is bending strength: how much load the beam takes before it breaks. A 2×10 Southern Yellow Pine joist carries a good deal more than a 2×10 SPF joist, because SYP runs MOR 14,500 psi against SPF at 10,500.

Density and Weight Estimation: Weight = (Width_in × Thickness_in × Length_ft × 12) / 1728 × Density_lb_per_ft³

All density values on this page are at roughly 12% moisture content, which is the equilibrium a board settles at indoors in a temperate climate. Green wood, freshly cut, can weigh 50 to 100% more purely from the water in it.

Worked Example: 2×6 Douglas Fir, 8 feet: Actual dimensions: 1.5" × 5.5" (nominal 2×6) Volume = 1.5 × 5.5 × 96 (inches) = 792 in³ = 0.458 ft³ Weight = 0.458 × 30 lb/ft³ = 13.8 lbs

One caution on the board-feet figure this returns. Enter the actual dimensions, as above, and you get 5.5 board-feet. Your lumber yard will charge you for 8, because board-feet are traded on the nominal size: (2 × 6 × 8) ÷ 12. Use the actual numbers when you want weight, and the nominal ones when you want the invoice.

Hardwood vs Softwood: Botanical Definition: Despite the names, hardwoods and softwoods are classified by seed type, not by hardness. Hardwoods are angiosperms, with enclosed seeds: oak, maple, walnut. Softwoods are gymnosperms, with naked seeds borne in cones: pine, fir, spruce.
Balsa is technically a hardwood and is one of the softest woods on earth, at a Janka of about 67 lbf. The naming has misled people for two centuries and nobody is going to fix it now.

Moisture Content Warning: Structural lumber must be dried to 19% MC or less (usually kiln-dried to 15%) before installation. Wet wood shrinks as it dries, causing warping, cupping, and nail pops in finished construction.