Wood Weight Calculator

How it works

Wood weight is volume times density, and the density of wood depends on two things: the species, captured by its specific gravity, and how much water the wood holds, its moisture content. The species list gives each wood's average specific gravity at 12% moisture content from the USDA Forest Products Laboratory Wood Handbook (FPL-GTR-282, 2021), Table 5-3.

Water adds weight, but drying also shrinks the wood, so the wood substance is packed into a smaller volume. The calculator follows the Wood Handbook's method: it converts the 12% specific gravity to a basic (green-volume) specific gravity, adjusts it for shrinkage at the moisture content you enter (Eq. 4-13, fiber saturation taken as 30%), and then applies density = water density × specific gravity × (1 + MC/100) (Eq. 4-14). Above 30% moisture content the volume stops changing and only the water weight grows.

Enter the actual dimensions of the boards or the total board feet. Board feet from a lumber tally are usually based on nominal rough sizes, so they overstate the volume of surfaced lumber a little.

Formula

1/Gb = 1/G12 + 0.265 × (1 − 12/30)
Gx   = 1 ÷ (1/Gb − 0.265 × (1 − MC/30))   for MC < 30%; Gx = Gb above
density (kg/m³) = 1000 × Gx × (1 + MC/100)
volume (cu ft)  = T (in) × W (in) × L (ft) × 12 × pieces ÷ 1728
                  or board feet × 144 ÷ 1728
weight          = density × volume

Example

A northern red oak board (G12 0.63) at 8% moisture content has a specific gravity of 0.644 on its 8% volume and a density of 1000 × 0.644 × 1.08 = 696 kg/m³ (43.4 lb/ft³). A board 1 in × 6 in × 8 ft is 1/3 cu ft, so it weighs about 14.5 lb (6.6 kg).

The Wood Handbook's own example: wood with a specific gravity of 0.605 at 12% moisture content (white ash) has a density of 1000 × 0.605 × 1.12 = 678 kg/m³. The Handbook gives 42.2 lb/ft³, read from its rounded table; converting the unrounded 677.6 kg/m³ gives 42.3 lb/ft³, which is what this calculator shows.

Assumptions and limitations

• Specific gravities are species averages from clear, defect-free test specimens. Individual boards vary: the Wood Handbook gives a coefficient of variation of about 10% for density within a species, so a real board can easily be 10% lighter or heavier.
• The shrinkage adjustment uses the Wood Handbook's general relation (volumetric shrinkage ≈ 26.5 × basic specific gravity, fiber saturation at 30%), not species-specific shrinkage data.
• The moisture content is taken as uniform through the board. Freshly kiln-dried or partly air-dried boards are often wetter inside than at the surface.
• Knots, finish, hardware and glue are not included. Treated lumber is heavier than untreated wood of the same species.
• Results are estimates for planning, shipping or handling. They are not a substitute for the design values and dead-load procedures of the applicable building code and design standard.

Frequently asked questions