How much does timber weigh? The question is an easy enough because that dry wood, yet more complicated to when freshly cut.

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Since water conveniently weighs about 1 g/cm3 , variable v temperature, specific gravity was derived as an table of contents metric to state the load of various other substances relative to water. The nice thing around using water as the recommendation measure was that beforehand scientists could easily classify materials by whether they to rise on water (specific gravity much less than 1.0) or even if it is they sink (specific gravity greater than 1.0).

With the particular gravity around 1.5, solid timber "substance", or lignocellulose as it is commonly called today, weighs about 1500 kg/m3 (93.6 lb/ft3), in ~ theoretical most…no air, water, or other fluids in cell pores, which would decrease the weight of the lumber per unit of volume. Wood additionally contains measurable amounts of necessary "extractives" such as such as terpenes, resins, and also polyphenols such as tannins, sugars, and also oils. In addition, inorganic compounds such together silicates, carbonates, and phosphates show up in the wood as "infiltrates" and an outcome in ash as the hardwood substance is decomposed. These extractives and infiltrates impregnate the lignocellulosic matrix and also fill parts of the cavities of the wood. Ash, which renders up 0.5% come 2.0% of many woods, has actually a details gravity the 1.6 come 2.8; the certain gravity that extractives varies relying on the substance. Together, the quantity of ash and also extractives in wood have the right to vary from trace quantities to 30% and also therefore influence the load of wood in different way according come species. 1

Thus far, we have actually been talking just of solid timber substance, i beg your pardon is no really timber as we recognize it. Wood of course, is comprised of cells, the which just the cabinet walls have the details gravity stated above. Yes, really woods, the amazing composite that cell matrix in infinitely different shapes, sizes, and also arrangements, lot like a sponge do of lignocellulose, have actually much lower details gravity 보다 the theoretical maximum due to the lot of room in the procession filled through air and water. And also like a sponge, most woods float, and also therefore have specific gravities less than 1.0; a few of the denser dry hardwoods room actually heavier than water and also sink. The most generally referenced "heaviest wood", lignum vitae (Guaiacum officinale), has a details gravity of 1.05 when green, which provides its weight about 1365 kg/m3, or 85 pounds per green cubic foot.

Now, green wood have the right to have moisture content anywhere from 30% (denser woods) to end 200% (lighter woods). Let"s talk around green timber in an ext detail.

First, the crazy moisture contents calculation that confounds so many start wood science students. How, they wonder, have the right to wood have much more than 100% moisture?

It can"t, that course. The moisture content calculation is merely a to compare of the mass of a sample of hardwood at any kind of given moisture to the mass once "oven-dry", or as soon as all the water has actually been removed from the sample. This is achieved by drying the lumber to a consistent weight in a activities oven held at 101 to 105 levels centigrade. The equation used for calculations is quite simple:

MC = (mgreen - mdry) / mdry (1)

So, to usage a an easy example, if a sample block of lumber weighs 50 grams at initial weighing, and also 40 grams after gift dried to 0% humidity content, climate the moisture content of the original sample was (50-40)/40, or 25%. Now, mean that original sample had actually weighed 100 grams. Then its initial moisture content would have actually been (100-40)/40, or 150%.

We view in this example that an increase in moisture content results in the raised weight of environment-friendly wood. This leader us additionally to the knowledge that sapwood, with its greater moisture content in the field, often weighs more than heartwood. Because that softwood, this is nearly always true. Hardwoods differ by species, and on average the moisture content in sapwood is only slightly higher. Table 4-1 of the 2010 hardwood Handbook2 offers the heartwood and also sapwood moisture contents of 40 north American hardwoods, and 28 phibìc American softwoods. For the types in the table, the hardwood heartwood averages 81% humidity content, while the hardwood sapwood averaged 83%; the softwood heartwood, however, averages just 60%, while the softwood sapwood averaged 152%!

A comparable situation exists between earlywood and latewood. Earlywood cells, created in the fast-growing at an early stage weeks of development when moisture movement is at its maximum, space necessarily larger with thinner cell walls to allow greater flow volume. As development slows, the later cells developed take top top a denser form with thicker cabinet walls and also smaller cell lumina. Therefore, those varieties or specimens the exhibit more comprehensive bands of earlywood (or diffuse-porous types that exhibition no evident latewood) will show more weight differential from eco-friendly to dry than will certainly those with far-ranging bands that latewood.

The most technically correct means to calculate weight of lumber gets somewhat tricky, due to the fact that the particular gravity the woods transforms with humidity content as soon as the moisture contents goes listed below 30%. 30% moisture content (plus or minus a pair of portion points, based upon the wood varieties and sample) is what we contact the fiber saturation allude of wood; over the fiber saturation point, the physical and also mechanical nature of wood perform not adjust as a function of humidity content. In various other words, the details gravity of timber does not adjust in timber that is above 30% humidity content. That is since the cellular framework of hardwood is "full" of what is called "bound water", the water chemically external inspection to the wood. The structure of the wood is totally expanded in ~ this point, and any added water that rises the moisture contents is "free" water residing in the cell pores and also lumina.

Once moisture content goes below 30%, however, all the totally free water has actually been released with evaporation, and also the bound water begins to be chemically moved from the wood substance. Together it walk so, the lumber cells start to shrink, again, simply as a sponge does as it dries out. And as it shrinks, the certain gravity the the hardwood gets higher, and also the hardwood becomes stiffer together the chemical properties change. Most varieties increase in thickness anywhere native 10 come 20% as they dried from 30% down to stove dry, 0%. (This, by the way, is why wood checks and also splits together it dries.) so another method of thinking about this is that the density of eco-friendly wood (that over 30%) is various (less) 보다 the thickness of the hardwood as stated in most references, which space usually provided as specific gravity in ~ 12% humidity content, because that the functions of aiding those who work-related with wood.

As you might surmise from the paragraph above, catching all the dynamics of changing wood density according to different moisture contents becomes pretty complex for anything but basic research. The researcher must have the ability to calculate the thickness of the hardwood at the moisture content of interest. For this reason, details gravity (which is always based top top a wood"s oven-dry mass) is normally expressed in one of three ways: 1) as particular gravity (oven-dry), i m sorry is the specific gravity the the wood once both mass and also volume room measured in ~ oven-dry; 2) as details gravity (basic, or green), which is the details gravity that wood when mass is measured in ~ oven-dry and volume is measure up green; and also as specific gravity (12%), which is the particular gravity of wood when mass is measured at oven-dry and volume is measured at 12% humidity content.

For the objective of our interest in calculating eco-friendly weights of wood, we deserve to ignore the complexities of timber shrinkage listed below 30% (as stood for by sg(oven-dry) and also sg(12%), and also use sg(basic) in our calculations. (Note: if you room interested in calculating weights of a kiln-dried woods, you should use the details gravity of the wood at that moisture content. The is when sg(12%) is most generally used.)

Basic certain gravity, sg(basic) or sg(green), is that estimated by compare of the wood"s mass at 0% come its volume when green (30% MC or above.) straightforward specific gravity is not given in most online recommendation pages, however they can be found for many types around the human being in Tables 5-3, 5-4, and 5-5 of the 2010 timber Handbook. (The simple specific gravity is identified by the at "green" moisture content in the tables, as opposed come the details gravities provided at 12% humidity content.) Other good sources for an easy specific gravity space the IWCS "Useful Woods the the World" books, and also online in ~ The timber Database. The most comprehensive tables of specific gravities, both an easy and at 12%, because that North American woods the I recognize of is compiled in "Specific Gravity and Other properties of Wood and Bark for 156 Tree varieties in north America", by Patrick Miles and also Brad Smith. This book is available totally free online.

To acquire on through the calculation of eco-friendly the magic the algebra, we transform Equation 1 over to

mgreen = mdry * (1 + MC) (2)

Recall the mdry is the massive of dry wood and also MC is the moisture content at which we wish to calculation the weight. We will use the mass of one cubic meter because that mdry, and for MC we have a choice: we could plug in an assumed moisture content, one taken native a green sample, or one taken native reference. There room not countless references ~ above the environment-friendly weight the wood; for this exercise, I have used Table 4-1 of the 2010 timber Handbook, which gives green load of heartwood and also sapwood for 40 north American hardwoods and 28 north American softwoods.

Let"s take the oaks and hickories first. Table 4-1 list 12 varieties of oaks and also hickories, and they average. 59 in basic specific gravity. Recall that certain gravity is thickness in grams every cubic centimeter (g/cm3); because the denominator of the details density is one cubic centimeter, and also assuming we desire to calculation the load of a cubic meter, we simply have to multiply 0.59 * 1000 to get 590 kilograms together the mdry for Equation 2.

Next, we need to recognize what moisture contents to mean for the varieties in question once green. We might then refer again to our Table 4-1 that the 2010 timber Handbook, and calculate the the average moisture content (heartwood and sapwood) for every 12 is 71%. Currently we have all we need. The calculation becomes:

Oak-Hickorygreen = 590 * (1 + 0.71) = 1009 kilograms/m3 , or 63 pounds/ft3

However, we know that through all the estimating and assuming we"ve been doing in these calculations, the our suggest estimate of 63 pounds per cubic foot is also precise. A far better way to state our expected environment-friendly weight that oaks and hickories would be to usage estimates based on variation roughly our average estimates. To keep it simple, ns calculate a Low selection estimate and also a High selection estimate for moisture content as 1/3 and 2/3 of the method between the proclaimed values of heartwood and sapwood humidity content. Having actually done that, we uncover that the shortest low variety estimate is because that sand hickory, in ~ 56%, and the highest possible high variety estimate is 85% for water hickory. Substituting these worths for the grand mean MC used above, and using the particular gravities because that the varieties from which we gain the MC variety values, us get:

Oak-Hickorygreenlow = 620 * (1 + 0.56) = 967 kilograms/m3 , or 60 pounds/ft3

Oak-Hickorygreenhigh = 610 * (1 + 0.85) = 1129 kilograms/m3 , or 70 pounds/ft3

So a correct statement in the original short article should have actually been the oaks and hickories average in between 60 and also 70 pounds every cubic foot green. If friend only have actually one estimate of eco-friendly moisture content to occupational with, just use the number because that the MC in the equation, as I execute in the next example.

The next varieties we take into consideration here is live oak, Quercus virginiana. Its simple density is 0.80. If we usage 80% as the moisture contents again (it isn"t provided on the timber Handbook table 4-1), our estimate of live oak"s green weight is:

Live Oakgreen = 800 * (1 + 0.8) = 1440 kilograms/m3, or 90 pounds/ft3

But we immediately an alert that this estimate is quite close to our ahead calculation that the maximum theoretical weight of wood. What"s wrong?

What we find is that there is a functional relationship in between the certain gravity the a wood and the moisture content it deserve to attain; in other words, at a details point, the density of the wood borders how much moisture it deserve to take in. Again a table indigenous the 2010 hardwood Handbook is helpful. Tables 4-6a and 4-6b offer us the relationship in between density the wood and moisture content. Unfortunately, the tables only go approximately a specific gravity of 0.7, where the highest feasible moisture contents is provided as 72%. However, by extrapolating the table by the tendency rate, we conclude that the highest possible moisture content of wood v a details gravity of 0.8 to be 52%.

So, our better estimate that the load of eco-friendly live oak becomes:

Live Oakgreen = 800 * (1 + 0.52) = 1216 kilograms/m3, or 76 pounds/ft3

This method works well because that all lumber species.

For those of girlfriend who simply can"t get sufficient of this kind of thing, I"ve emerged an Excel spreadsheetthat calculates dry and also green lumber weight the different species from particular gravity and moisture content data native the miscellaneous tables I"ve alluded come in this article. Also, if girlfriend have eco-friendly moisture contents data on types outside of phibìc America, and you feel prefer sharing the data, please send it on and also I will add those species with the appropriate calculations come the spreadsheet.


Wood: its Structure and also Properties. Volume 1. Edited by F.F. Wangaard. 1981. The Pennsylvania State university Press. Web page 199.Wood Handbook: timber as an engineering Material. 2010 Edition. The Forest assets Society.

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Green wood Weight Calculator

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