Methodology & sources

Calculation formulas

Every calculator on this site uses one of the formulas below, exactly as written. Inputs are inches unless noted; MC = moisture content in percent.

board feet              = (thickness × width × length_in) ÷ 144 × quantity
movement ΔD             = D × (S ÷ 30 ÷ 100) × ΔMC
weight (lb)             = (thickness × width × length_in) ÷ 1728 × quantity × density (air-dry)
density (air-dry, 12%)  = 62.4 × specific gravity (12% MC) × 1.12   [primary — displayed]
density (ovendry basis) = 62.4 × specific gravity (12% MC)          [secondary]
kg/m³                   = lb/ft³ × 16.0185
lb per bd ft            = density (lb/ft³) ÷ 12
T/R ratio               = tangential shrinkage ÷ radial shrinkage

Source tables and data basis

Every value traces to a specific FPL-GTR-282 table. The exact tables, and the basis each was recorded on, are:

Shrinkage — Tables 4-3 (domestic) and 4-4 (imported). Percentages are total shrinkage from green to oven-dry (Table 4-3/4-4 footnote: “expressed as a percentage of the green dimension”). This is not green-to-12% or kiln-dry movement; the movement calculator spreads it across the fiber-saturation point to estimate in-service change.

Specific gravity — Tables 5-3b (domestic) and 5-5b (imported), and the basis differs between them. Domestic specific gravity is on an ovendry-weight, volume-at-12%-MC basis. Imported specific gravity is a single “estimated average clear-wood specific gravity” (ovendry weight) drawn from world literature, with one value per species rather than separate green and 12% values.

Janka hardness — Tables 5-3b / 5-5b, side hardness at 12% MC, read directly in pounds-force from the inch–pound tables (no newton-to-lbf conversion). A few species whose 12% cell is blank fall back to the green side-hardness value, noted per species.

Density is computed, not tabulated — and two figures are kept. The handbook has no per-species density table. The base computation, 62.4 × specific gravity (12% MC), yields an ovendry-weight density: the mass of oven-dry wood substance per cubic foot of 12%-MC wood, excluding the roughly 12% of bound water a dried board actually carries. The site's primary, displayed figure is therefore air-dry density at 12% MC = 62.4 × SG(12%) × 1.12, which adds that bound-water mass back — matching how dried lumber is actually weighed and handled, and how lumber references quote density. The ovendry figure is shown as secondary small print on each species page. For imported species the same ×1.12 convention is applied to their single literature-average specific gravity (see the SG caveat above), so their air-dry figures inherit that basis uncertainty.

Equilibrium moisture content — Table 13-1, monthly EMC (%) for 50 U.S. locations under outdoor exposure (data through 2010). The per-species “seasonal movement by city” examples use each city's driest and most-humid month from this table; an indoor, climate-controlled space swings less.

The movement approximation and its limits

The movement formula spreads a species' total green→oven-dry shrinkage (S) linearly across the fiber saturation point, taken by convention as 30% MC — so S ÷ 30 is the shrinkage per 1% of moisture change. This is the standard workshop estimate and tracks the Wood Handbook's dimensional-change equation closely across the 5–15% MC range where interior woodwork lives. It is less reliable near the extremes (very green or oven-dry wood), and individual boards vary with grain angle, density, and drying history; treat results as planning figures, not guarantees.

Unit conventions

Shrinkage percentages are total, from green to oven-dry. Specific gravity, Janka side hardness, and computed density are on the 12% moisture-content basis described above. Quarter-system thickness (4/4, 5/4, 6/4, 8/4) converts to inches by dividing by 4. Where the Wood Handbook strength tables list no matched value for a species that does have shrinkage data, the missing field is shown as “—” rather than estimated.

Update policy

The Wood Handbook is a static reference document (2021 edition); its values do not drift, so there is no scheduled data refresh. The dataset is checked once a year against published errata, and immediately when a reader reports a discrepancy. Each data extraction records its source, retrieval date, and row counts.