How Much Does a 2x4 Weigh? (and Other Common Questions)
In order to find the weight of your 2 x 4, assuming it’s construction lumber, you first have to establish what kind of wood it is. Fir, spruce, Douglas fir, Hemlock, Larch, Pine, or whatever else it may be all have their very own particularities in hardness, weight, flexibility, density affecting their specific gravity and density.
The weight of your sample should be quite easy to calculate if you have the right information about it. Once you have its specie identified, you can easily find crucial pieces of data such as density or actual specific gravity (SG) needed to calculate the weight.
Facts About Density and Weight
Density is the mass (in pounds) per unit volume (in cubic feet) of a substance (lb/cf). Since it contains more water within its fibers, a one cubic foot sample of a tree that’s just been cut and is at 80% MC (moisture content) weighs more than the same size sample of the same tree once it has been transformed into lumber and has reached an equilibrium moisture content of 12%. It is safe to say then that the density of wood varies with its moisture content.
When looking up the density of a piece of wood of which you need to determine the weight, make sure that the source of the info specifies at which percentage MC it is based on, the info is useless if it doesn’t. If the lumber’s been around the shop for a few months or years, it has probably reached an equilibrium point with the relative humidity of the air surrounding it—it is called the equilibrium moisture content (MC) and that’s most likely the MC point at which you’re seeking the weight.
Specific Gravity—Botanical vs Woodworking
While looking up the specifications of wood, you’ll come across different terms such as specific gravity, basic specific gravity, and actual specific gravity.
Oven-dried wood refers to lumber further dried at 0% moisture content, where all of its moisture has been extracted from it. In botany, the specific gravity is calculated on this oven-dried density in relation to its volume when completely saturated with water at above 30% MC—it’s called the “Basis Specific Gravity”, but is not practical in woodworking however since we deal with wood seasoned at 12% EMC. The problem, however, lies in that it creates a lot of different standards all referenced as SG but none of which is based on the same norm and more often than not doesn’t specify at what MC level it’s based on.
Specific gravity is one of the most abused and misused terms in woodworking, so be careful when seeking your info. As references for woodworkers, sources such as the Forest Products Laboratory of Wisconsin (US Forest Service), “wood-database.com” has hundreds of worldwide species of wood listed with the “actual SG at 12% MC”. Just keep in mind though that although it is the best guide available to do as accurate a job as possible, it is not an exact science—sapwood and heartwood have different characteristics, same as a specie from coastal area compared to the same specie from farther inland.
Specific gravity is the ratio of the weight of a specific volume of wood—for instance, one cubic foot—to the weight of the same cubic foot volume of water, which is the standard at 62.4 lbs/ft³. Specific gravity is a dimensionless quantity and isn’t expressed in unit.
Weight of a Red Spruce 2x4
2” x 4” nominal means that the actual size of your lumber is less, around 1-1/2” x 3-1/2”. Take the actual measurements as accurately as possible and calculate the volume.
Cu. ft. = Thickness (Ft) x Width (Ft) x Lenght (let’s use 12ft 6in. for an example).
Cu. ft. = (1-1/2”/ 12) x (3-1/2”/ 12) x 12.5’
Cu. ft. = 0.125’ x 0.292’ x 12.5’
The volume of the 2 x 4 = 0.456 Cu. ft.
A—With a density (at 12% MC) of 27 lbs/c.f. and a total volume of 0.456 cu. ft.
weight = 27 lbs x 0.456 c.f. = 12.3 lbs total.
B—If all you can find is the actual SG of 0.43, you can find the density with—
Density = 0.43 x density of water (62.4 lbs/c.f.)
Density = 26.8 lbs/c.f.
Weight = 26.8 x 0.456 c.f. = 12.2 lbs total.
As mentioned before, it’s as close as you get with the type of material your working with, but using the actual density at 12% MC is a more accurate method than even with the actual specific gravity.