American elm (Ulmus americana) in numbers: hardness, weight, strength, shrinkage, movement and decay resistance, taken from the tables of the USDA Forest Products Laboratory’s Wood Handbook, followed by what the wood is like to work and what it is used for. The values are averages from small, clear, straight-grained test specimens; real boards with knots, sloping grain or a different moisture content will differ.
| Property | American elm |
|---|---|
| Janka side hardness, 12% moisture | 830 lbf (3,692 N) |
| Janka side hardness, green | 620 lbf |
| Hardness rank | harder than 71 of the 168 woods with a 12% hardness value in our database |
| Density at 12% moisture | 35.0 lb/ft³ (560 kg/m³) |
| Weight per board foot (12%) | 2.91 lb |
| Specific gravity (ovendry weight, green volume) | 0.46 |
| Specific gravity at 12% moisture | 0.50 |
| Bending strength (modulus of rupture), 12% | 11,800 psi |
| Stiffness (modulus of elasticity), 12% | 1.34 million psi |
| Crushing strength (compression parallel to grain), 12% | 5,520 psi |
| Shrinkage green to ovendry: radial / tangential / volumetric | 4.2% / 9.5% / 14.6% |
| Tangential / radial shrinkage ratio | 2.26 |
| Dimensional change per 1% moisture (radial / tangential) | 0.00144 / 0.00338 |
| Impact bending (drop height to failure), 12% | 39 in. |
| Heartwood decay resistance | slightly or nonresistant |
The species in this group
Lumber is often sold under a group name. These are the species the Wood Handbook reports for this group, with the same properties side by side.
| Species | Janka (lbf) | Density (lb/ft³) | Bending (psi) | Stiffness (Mpsi) | Crushing (psi) | Shrink T/R (%) | Decay resistance |
|---|---|---|---|---|---|---|---|
| American elm Ulmus americana | 830 | 35.0 | 11,800 | 1.34 | 5,520 | 9.5 / 4.2 | slightly or nonresistant |
| Rock elm Ulmus thomasii | 1,320 | 44.1 | 14,800 | 1.54 | 7,050 | 8.1 / 4.8 | slightly or nonresistant |
| Slippery elm Ulmus rubra | 860 | 37.1 | 13,000 | 1.49 | 6,360 | 8.9 / 4.9 | slightly or nonresistant |
What it is
Six species of elm grow in the eastern United States: American (Ulmus americana), slippery (U. rubra), rock (U. thomasii), winged (U. alata), cedar (U. crassifolia) and September elm (U. serotina). American elm is also known as white elm, slippery elm as red elm, rock elm as cork elm and winged elm as wahoo. American elm is threatened by two diseases, Dutch elm disease and phloem necrosis, which have killed hundreds of thousands of trees.
Elm sapwood is nearly white and the heartwood light brown, often tinged with red. Elm is divided into two general classes by the weight and strength of the wood: soft elm (American and slippery elm) and hard elm (rock, winged, cedar and September elm), which is somewhat heavier.
Working properties
Soft elm is moderately heavy, moderately hard and stiff, and high in shock resistance, and elm in general has excellent bending qualities. American elm shrinks 9.5% tangentially from green to ovendry, and in service a flatsawn board changes width by about 0.338% for each 1% change in moisture content.
Weight and density
At 12% moisture content american elm weighs about 35.0 lb per cubic foot, so one board foot (144 cubic inches) weighs about 2.91 lb. An 8 ft board of actual size 3/4 × 5-1/2 in. (a 1×6) holds 0.229 cubic feet and weighs about 8.0 lb; an 8 ft piece 1-1/2 × 3-1/2 in. (a 2×4 size) weighs about 10.2 lb. Green wood is much heavier because of the water it holds.
Density here is ovendry weight plus 12% water, divided by volume at 12% moisture content (Wood Handbook Eq. 4-12: density = specific gravity at 12% × 62.43 lb/ft³ × 1.12).
Wood movement
The Wood Handbook gives dimensional change coefficients for each species: the fraction of its width a board gains or loses for every 1% change in moisture content, between about 6% and 14%. For american elm they are 0.00338 across a flatsawn face (tangential) and 0.00144 across a quartersawn face (radial).
Worked example: a flatsawn board 7-1/4 in. wide (a nominal 1×8) that goes from 6% moisture content in a heated winter house to 12% in a humid summer changes width by 7.25 × 0.00338 × 6 = 0.147 in. (about 5/32 in.). The same board quartersawn moves 0.063 in. (about 1/16 in.). Allow for this in panels, tabletops and floors; the wood movement calculator works it out for any size and moisture range.
How it compares
| Species | Janka (lbf) | Density (lb/ft³) | Bending (psi) | Stiffness (Mpsi) | Tangential shrink (%) | Decay resistance |
|---|---|---|---|---|---|---|
| American elm | 830 | 35.0 | 11,800 | 1.34 | 9.5 | slightly or nonresistant |
| Hackberry | 880 | 37.1 | 11,000 | 1.19 | 8.9 | slightly or nonresistant |
| White ash | 1,320 | 42.0 | 15,000 | 1.74 | 7.8 | slightly or nonresistant |
| Northern red oak | 1,290 | 44.1 | 14,300 | 1.82 | 8.6 | slightly or nonresistant |
| American sycamore | 770 | 34.3 | 10,000 | 1.42 | 8.4 | slightly or nonresistant |
| Sweetgum | 850 | 36.4 | 12,500 | 1.64 | 10.2 | slightly or nonresistant |
Uses
Today elm lumber and veneer are used mostly for furniture and decorative panels, and hard elm is preferred where strength is needed. Historically elm went into boxes, baskets, crates, slack cooperage, furniture, agricultural supplies and implements, caskets and burial boxes, and wooden parts of vehicles.
Frequently asked questions
How hard is elm?
American elm averages 830 lbf (3,692 N) on the Janka test at 12% moisture content. Rock elm, one of the hard elms, is much harder at 1,320 lbf.
What is the difference between soft elm and hard elm?
Soft elm is American and slippery elm; hard elm is rock, winged, cedar and September elm, which are somewhat heavier. In the group table, rock elm is heavier, harder and stronger in bending than American elm.
Is elm good for bending?
Yes. The Wood Handbook says elm has excellent bending qualities.
Is elm rot resistant?
No. Elm heartwood is in the slightly or nonresistant decay class, so it needs preservative treatment or a protected location outdoors.
Sources
- USDA Forest Products Laboratory. Wood Handbook: Wood as an Engineering Material. General Technical Report FPL-GTR-190, 2010. Chapter 2 (species descriptions), Chapter 4 (Tables 4-3, 4-4 shrinkage; Eq. 4-7, 4-9, 4-12 density), Chapter 5 (Tables 5-3b, 5-5b strength and hardness), Chapter 13 (Table 13-5 dimensional change coefficients), Chapter 14 (Table 14-1 decay resistance)
- USDA Forest Products Laboratory. Wood Handbook, 2021 edition (FPL-GTR-282)
Last reviewed: 24 October 2026. Numbers are generated from our parsed copy of the Handbook tables, so every page uses the same data. Values marked * are estimates computed with the Handbook’s own equations. Spotted an error? Please let us know.