Wood density is the mass of wood per unit volume, and it is the best single predictor of strength and stiffness in clear, defect-free wood. For pallet species the 12% moisture density ranges from roughly 390 kg/m³ (24 lb/ft³) for eastern white pine to about 760 kg/m³ (47 lb/ft³) for white oak, with bending strength rising almost in proportion.
How to read the table
The most widely cited source for clear-wood properties is the Wood Handbook: Wood as an Engineering Material, published by the USDA Forest Products Laboratory (FPL). It tabulates specific gravity (relative density), modulus of rupture and modulus of elasticity from small, defect-free samples tested to a standard method.
- Specific gravity (SG): oven-dry mass divided by the mass of the same volume of water. It is dimensionless; SG 0.50 means half the density of water when dry.
- Density at 12% moisture content: in this article, approximated as SG × 1.12 × 1000 kg/m³, which includes the water mass at 12% moisture and ignores the small shrinkage-related volume effects. Values are rounded to the nearest 10 kg/m³ and are estimates, not tabulated Wood Handbook figures.
- Modulus of rupture (MOR): the bending stress at failure, a measure of strength. Higher MOR means the board carries more load before breaking.
- Modulus of elasticity (MOE): stiffness. It controls how much a deck board or stringer sags under a given load.
Moisture content strongly affects every figure: green wood is weaker and heavier than dry wood. See wood moisture content for how it is measured and controlled.
Table of common species at 12% moisture content
Values below are for clear wood at 12% moisture content, taken from Wood Handbook Table 5-3 (metric version) as reproduced by an engineering education provider; densities are the author's calculation as described above.
| Species | Type | SG (12%) | Approx. density at 12% (kg/m³) | MOR (MPa) | MOE (GPa) |
|---|---|---|---|---|---|
| Eastern white pine | Softwood | 0.35 | 390 | 59 | 8.5 |
| Sitka spruce | Softwood | 0.40 | 450 | 70 | 10.8 |
| Yellow-poplar | Hardwood | 0.42 | 470 | 70 | 10.9 |
| Douglas-fir, coast | Softwood | 0.48 | 540 | 85 | 13.4 |
| Loblolly pine | Softwood | 0.51 | 570 | 88 | 12.3 |
| Paper birch | Hardwood | 0.55 | 620 | 85 | 11.0 |
| Longleaf pine | Softwood | 0.59 | 660 | 100 | 13.7 |
| Northern red oak | Hardwood | 0.63 | 710 | 99 | 12.5 |
| White oak | Hardwood | 0.68 | 760 | 105 | 12.3 |
Metric to imperial: 1 MPa = 145 psi, and 1 GPa = 145,000 psi. For instance, loblolly pine at 88 MPa is about 12,800 psi, and 12.3 GPa is about 1.79 million psi.
What the numbers mean for pallets
Density is not the whole story. Strength rises with density, but stiffness does not follow as neatly. The table shows that yellow-poplar and Sitka spruce have nearly identical strength, and that white oak is much denser than longleaf pine while its MOE is lower. Species selection therefore needs more than a density ranking.
Clear-wood values are the ceiling, not the design value. Real pallet boards contain knots, slope of grain, wane, checks and other defects that cut strength well below the figures above. The effect is regulated by lumber grading rules and timber defect limits, and pallet design standards apply reduction factors for variability and long-term load. Never use the table values directly as allowable stresses.
Heavier wood adds weight and nail difficulty. A dense hardwood pallet may carry more but also weighs more, raising freight cost, and it is harder to nail without splitting; see pallet weight guide and pallet nails and fasteners.
Stiffness often governs. Deck boards and stringers on a rack beam fail by excessive deflection long before they break, so MOE can matter as much as MOR. Load testing is described in pallet testing standards.
Typical species groups in pallet making
Pallet materials depend on what is locally available and cheap:
| Region | Common pallet wood | Notes |
|---|---|---|
| Northern and Central Europe | Norway spruce, Scots pine | Light, easy to nail; see spruce and fir |
| Southeastern United States | Southern yellow pines (loblolly, longleaf, shortleaf, slash) | Strong, common in new pallets; see southern yellow pine |
| Southern Hemisphere | Radiata pine | Plantation softwood; see radiata pine |
| Eastern United States | Oak, mixed hardwoods | Large share of US pallet lumber is hardwood; see softwood vs hardwood pallets |
| Eastern Europe, Asia | Birch, poplar, mixed species | Light hardwoods used for blocks and boards; see poplar and birch |
Spruce, Scots pine and radiata pine are not in the table above because the Wood Handbook covers species grown in the United States; their values should be taken from European (EN 338 or EN 408) or national data. The overview of choices is in pallet wood species.
Limits of the data
- The values come from small, clear specimens tested under standardized conditions. Variation between trees, sites and growth rates is significant; the Wood Handbook itself reports coefficients of variation.
- Fast-grown plantation wood, with wide rings and a high proportion of juvenile wood, is usually lighter and weaker than the table values for the same species name.
- Duration of load matters. A load that a board carries for a minute may cause creep and failure over months of rack storage.
- Below the fiber saturation point (roughly 25 to 30% moisture) wood gains strength and stiffness as it dries, which is one reason kiln drying improves quality.
Frequently asked questions
Which wood is strongest for pallets?
Among the species in the table, white oak and longleaf pine have the highest bending strength. In practice the strongest species is not always the best choice, because heavier wood costs more to ship and nail.
What is the density of pine wood?
Pines cover a wide range. In the Wood Handbook, eastern white pine is about 390 kg/m³ at 12% moisture, loblolly pine about 570 kg/m³ and longleaf pine about 660 kg/m³, based on the calculation described here.
Can density be used to estimate pallet weight?
Yes, for a rough estimate: multiply timber volume by density at the actual moisture content. Wet wood weighs much more than the 12% figures.
Are these values safe to use for engineering design?
No. They are clear-wood averages. Structural design uses graded lumber values with safety factors, or tested pallet designs.
Sources
- Wood Handbook: Wood as an Engineering Material (FPL-GTR-190) — USDA Forest Products Laboratory
- Wood as an Engineering Material: Mechanical Properties of Wood (Table 5-3 reproduction) — CED Engineering
- How Much Load Can My Pallet Carry? — Virginia Tech Center for Packaging and Unit Load Design