Wood species density and behaviour
Density is the one number that predicts most of what a builder cares about: weight, hardness, how much the board moves, how well it holds a screw, and how quickly it dulls a blade. It is also the number most material guides leave out.
The table
Densities are averages at 12% moisture content, from published species data. The 2×8×12 column is actual dressed volume (0.906 ft³) multiplied by density, so the weights are comparable to each other and to the calculator.
| Species | lb/ft³ | 2×8×12 | Movement | Rot resistance |
|---|---|---|---|---|
| Western red cedar | 23 | 21 lb | Low–moderate | High |
| Eastern white pine | 25 | 23 lb | Moderate | Low |
| Redwood (young growth) | 26 | 24 lb | Low | High |
| Spruce-pine-fir | 27 | 24 lb | Moderate–high | Low, needs treatment |
| Hem-fir | 28 | 25 lb | Moderate | Low, needs treatment |
| Alaskan yellow cedar | 28 | 25 lb | Low | Very high |
| Yellow poplar | 28 | 25 lb | Moderate | Low |
| Douglas fir (coast) | 34 | 31 lb | Moderate | Moderate |
| Black cherry | 35 | 32 lb | Moderate | Moderate |
| Southern yellow pine | 37 | 34 lb | High | Low, needs treatment |
| Black walnut | 38 | 34 lb | Moderate | Moderate |
| Teak | 41 | 37 lb | Low | Very high |
| Ash | 42 | 38 lb | High | Low |
| Red oak | 44 | 40 lb | High | Low |
| Hard maple | 44 | 40 lb | Moderate–high | Low |
| White oak | 47 | 43 lb | Moderate | High |
| Hickory | 50 | 45 lb | High | Low |
| Cumaru | 68 | 62 lb | Low | Very high |
| Ipe | 69 | 63 lb | Low | Very high |
Movement is not the same as density
It is tempting to assume denser means more stable, and for tropical hardwoods that happens to be true. But red oak and hickory are both dense and both move a great deal, while western red cedar is light and moves very little. Movement is a property of the cell structure, not the mass.
This is why deck board gaps are specified by material rather than by species weight: ⅛″ for dense tropical hardwood, ¼″ for treated pine, and whatever the clip system specifies for composite — which absorbs almost no water and therefore barely moves at all.
Rot resistance, and why treatment exists
The heartwood of a naturally durable species resists decay because of extractives the tree deposited while growing. That resistance does not extend to the sapwood, which is why a "cedar" deck board with a wide sapwood face can rot while the board beside it does not. Pressure treatment solves the same problem chemically by forcing preservative into the sapwood, which is why treated pine is specified by retention level rather than by species.
Nothing resists decay when it is wet and buried. A durable species in soil contact still fails; the mechanism is just slower. The details that keep wood dry — flashing, post bases, a 6″ clearance from grade — matter more than the species in the end.
Choosing by density
- Under 30 lb/ft³ — cedar, pine, fir, spruce. Easy to work, light to handle, needs protection or treatment, dulls blades slowly.
- 30–45 lb/ft³ — the middle band: oak, ash, maple, Douglas fir, walnut. Dense enough to hold a screw without splitting if you pre-drill, still workable with standard tools.
- Over 60 lb/ft³ — ipe, cumaru, teak. A 30-year surface that needs carbide tooling, stainless fasteners, pre-drilled pilot holes, and two people to place a board.
If you are choosing a deck surface, the trade is not really density against price — it is maintenance interval against money. A treated pine deck needs re-coating every one to two years; ipe needs oiling every year or two but will outlast two pine decks. See the material guide for that comparison in cost terms.
What density does not tell you
- Not a grading table. Density says nothing about allowable span. Two boards of the same species, size and density can carry different loads because of grade.
- Not a hardness chart. Janka hardness is a separate test with its own scale, and it is not proportional to density across species.
- Not species identification. If you need to know what a board actually is, density is a weak signal — grain, odour and end-grain structure are better.
Questions people actually ask
What is the density of pressure-treated lumber?
The species behind it is usually southern yellow pine at about 37 lb/ft³, but treated stock is sold wet, at 25–30% moisture, which puts a 2×8×12 near 40 lb at the yard rather than the 34 lb dry figure.
Is cedar strong enough for a deck?
For decking, yes. For structure, western red cedar is a low-density species and its allowable spans are shorter than Douglas fir or southern pine at the same size — check the span table for the specific species and grade, not just the size.
Why is ipe so expensive?
Density, growth rate and supply. Ipe is a slow-growing tropical hardwood with very high density and natural durability, which means fewer board feet per tree and much higher tool wear during milling.
Does density affect screw holding?
Yes. Dense species hold better but split more easily, so pilot holes become mandatory rather than optional. In ipe and cumaru, driving a screw without a pilot hole will split the board along the grain.
Which species is best for deck framing?
Whatever the local span table is built around — commonly southern yellow pine or Douglas fir in treated form. Framing is selected by grade and species group for span, not by density or appearance, because it will never be seen.