Data & method

Every number on TimberLedger comes from one public source, the USDA Forest Products Laboratory’s Wood Handbook. We rank and compare those numbers; we do not change them.

Source

Forest Products Laboratory. 2010. Wood handbook—Wood as an engineering material. General Technical Report FPL-GTR-190. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 508 p.

Tables used: Table 4-3 (shrinkage, domestic), Table 4-4 (shrinkage, imported), Table 5-3b (strength, U.S. woods, inch-pound), Table 5-5b (strength, imported woods, inch-pound), Tables 5-3a and 5-5a (metric) used only to cross-check unit conversions, Chapter 2 Scientific Name Index (botanical names of U.S. species). The Wood Handbook is a work of the U.S. Government and is in the public domain. Values are as published in the 2010 edition; a 2021 edition exists and may revise some figures.

What the values mean

Strength values are averages from small, clear, straight-grained specimens tested green and at 12% moisture content. They are not design values for structural use and do not account for knots, grade or moisture. Imported woods’ figures come from world literature and may not be species averages; the handbook does not state the specific-gravity basis for that table.

Calculations

Hardness vs red oak

Side hardness ÷ northern red oak’s 1,290 lbf × 100.

Stiffness-to-weight

Modulus of elasticity ÷ specific gravity.

Strength-to-weight

Modulus of rupture ÷ specific gravity.

T/R ratio

Tangential shrinkage ÷ radial shrinkage. Closer to 1 means a board is less likely to cup.

Board width change

6 inches × shrinkage percentage, green to oven-dry: tangential for flatsawn boards, radial for quartersawn.

Substitutes

The nearest species on six standardized properties, weighted equally.

Ranks compare the 155 species on this site; species without published hardness, strength and shrinkage are not included.

The measures on each species page

Janka hardness

Resistance to dents and wear. Force to press a steel ball halfway in.

Density

Specific gravity: oven-dry weight over green volume. Heavier woods are usually harder.

Bending strength

Modulus of rupture: the load a beam carries before it breaks.

Stiffness

Modulus of elasticity: how little it bends under a load.

Shrinkage across the face

Tangential shrinkage, green to oven-dry. Lower means less movement.

Cupping tendency

Tangential ÷ radial shrinkage. The closer to 1, the flatter a board stays.

Strip plots

Each grey tick is one of the 155 woods, lowest on the left; the dark tick is the median of the wood’s group and the red line is the wood itself. Measures are listed with the one where the wood is most extreme first.

Board drawings

End view of a 6 × 1½-inch board, green (dashed) and oven-dry, with shrinkage drawn three times life size. Flatsawn boards lose width by tangential shrinkage, quartersawn boards by radial shrinkage.

Highlights

The short list under each wood’s Janka figure is chosen from its own data: records and near-records among all 155 woods or within its group or family, ties, a hardness well above or below what its density predicts (more than one standard deviation, 230 lbf, from the fitted line), unusual change in hardness on drying, and large gaps to its group median. The most unusual facts come first.

Laboratory properties

Modulus of rupture

Bending strength: the load a beam carries before it breaks.

Modulus of elasticity

Stiffness: how little a beam bends under load.

Work to maximum load

Energy absorbed in bending up to the maximum load.

Impact bending

Drop height of a 50-lb hammer.

Compression parallel to grain

Crushing strength, end-on.

Compression perpendicular

Crushing across the grain.

Shear parallel to grain

Resistance to splitting along the grain.

Tension perpendicular

Pulling apart across the grain.

Side hardness

The Janka test.

Small, clear, straight-grained specimens are tested green and again at 12% moisture content. Some woods, mostly imports, have only 12% values in the handbook.