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Calculating the Green Weight of Wood Species

How much does wood weigh? The question is simple enough for dry wood, but more difficult when wood is freshly cut.

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Updated:

March 8, 2023

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Since water conveniently weighs about 1 g/cm³, variable with temperature, specific gravity was derived as an index metric to state the weight of other substances relative to water. The nice thing about using water as the reference measure was that early scientists could easily classify materials by whether they float on water (specific gravity less than 1.0) or whether they sink (specific gravity greater than 1.0).

With the specific gravity around 1.5, solid wood "substance", or lignocellulose as it is commonly called today, weighs around 1500 kg/m³ (93.6 lb/ft³), at theoretical most…no air, water, or other fluids in cell pores, which would decrease the weight of the wood per unit of volume. Wood also contains measurable quantities of organic "extractives" such as such as terpenes, resins, and polyphenols such as tannins, sugars, and oils. In addition, inorganic compounds such as silicates, carbonates, and phosphates appear in the wood as "infiltrates" and result in ash as the wood substance is decomposed. These extractives and infiltrates impregnate the lignocellulosic matrix and fill parts of the cavities of the wood. Ash, which makes up 0.5% to 2.0% of most woods, has a specific gravity of 1.6 to 2.8; the specific gravity of extractives varies depending on the substance. Together, the amount of ash and extractives in wood can vary from trace amounts to 30% and therefore affect the weight of wood differently according to species.¹

Thus far, we have been talking only of solid wood substance, which is not really wood as we know it. Wood of course, is comprised of cells, of which only the cell walls have the specific gravity stated above. Actual woods, the amazing composite of cell matrix in infinitely different shapes, sizes, and arrangements, much like a sponge made of lignocellulose, have much lower specific gravity than the theoretical maximum due to the amount of space in the matrix filled with air and water. And like a sponge, most woods float, and therefore have specific gravities less than 1.0; a few of the denser tropical hardwoods are actually heavier than water and sink. The most commonly referenced "heaviest wood", lignum vitae (Guaiacum officinale), has a specific gravity of 1.05 when green, which makes its weight about 1365 kg/m³, or 85 pounds per green cubic foot.

Now, green wood can have moisture content anywhere from 30% (denser woods) to over 200% (lighter woods). Let's talk about green wood in more detail.

First, that crazy moisture content calculation that confounds so many beginning wood science students. How, they wonder, can wood have more than 100% moisture?

It can't, of course. The moisture content calculation is simply a comparison of the mass of a sample of wood at any given moisture to its mass when "oven-dry", or when all the water has been removed from the sample. This is accomplished by drying the wood to a constant weight in a laboratory oven held at 101 to 105 degrees centigrade. The equation used for calculations is quite simple:

MC = (m_green - m_dry) / m_dry (1)

So, to use a simple example, if a sample block of wood weighs 50 grams at original weighing, and 40 grams after being dried to 0% moisture content, then the moisture content of the original sample was (50-40)/40, or 25%. Now, suppose that original sample had weighed 100 grams. Then its original moisture content would have been (100-40)/40, or 150%.

We see in this example that an increase in moisture content results in the increased weight of green wood. This leads us also to the understanding that sapwood, with its higher moisture content in the field, often weighs more than heartwood. For softwood, this is practically always true. Hardwoods vary by species, and on average the moisture content in sapwood is only slightly higher. Table 4-1 of the 2010 Wood Handbook² gives the heartwood and sapwood moisture contents of 40 North American hardwoods, and 28 North American softwoods. For the species in the table, the hardwood heartwood averages 81% moisture content, while the hardwood sapwood averaged 83%; the softwood heartwood, however, averages only 60%, while the softwood sapwood averaged 152%!

A similar situation exists between earlywood and latewood. Earlywood cells, formed in the fast-growing early weeks of growth when moisture movement is at its maximum, are necessarily larger with thinner cell walls to allow higher flow volume. As growth slows, the later cells formed take on a denser form with thicker cell walls and smaller cell lumina. Therefore, those species or specimens that exhibit wider bands of earlywood (or diffuse-porous species that exhibit no apparent latewood) will show more weight differential from green to dry than will those with significant bands of latewood.

The most technically correct way to calculate weight of wood gets somewhat tricky, because the specific gravity of woods changes with moisture content once the moisture content goes below 30%. 30% moisture content (plus or minus a couple of percentage points, based on the wood species and sample) is what we call the fiber saturation point of wood; above the fiber saturation point, the physical and mechanical properties of wood do not change as a function of moisture content. In other words, the specific gravity of wood does not change in wood that is above 30% moisture content. That is because the cellular structure of wood is "full" of what is called "bound water", the water chemically bonded to the wood. The structure of the wood is fully expanded at this point, and any additional water that increases the moisture content is "free" water residing in the cell pores and lumina.

Once moisture content goes below 30%, however, all the free water has been released through evaporation, and the bound water begins to be chemically driven from the wood substance. As it does so, the wood cells begin to shrink, again, just as a sponge does as it dries out. And as it shrinks, the specific gravity of the wood gets higher, and the wood becomes stiffer as the chemical properties change. Most species increase in density anywhere from 10 to 20% as they dry from 30% down to oven dry, 0%. (This, by the way, is why wood checks and splits as it dries.) So another way of thinking about this is that the density of green wood (that above 30%) is different (less) than the density of the wood as stated in most references, which are usually given as specific gravity at 12% moisture content, for the purposes of aiding those who work with wood.

As you may surmise from the paragraph above, capturing all the dynamics of changing wood density according to different moisture contents becomes pretty complicated for anything but basic research. The researcher must be able to calculate the density of the wood at the moisture content of interest. For this reason, specific gravity (which is always based on a wood's oven-dry mass) is usually expressed in one of three ways: 1) as specific gravity (oven-dry), which is the specific gravity of the wood when both mass and volume are measured at oven-dry; 2) as specific gravity (basic, or green), which is the specific gravity of wood when mass is measured at oven-dry and volume is measured green; and as specific gravity (12%), which is the specific gravity of wood when mass is measured at oven-dry and volume is measured at 12% moisture content.

For the purpose of our interest in calculating green weights of wood, we can ignore the complexities of wood shrinkage below 30% (as represented by sg(oven-dry) and sg(12%), and use sg(basic) in our calculations. (Note: if you are interested in calculating weights of a kiln-dried woods, you must use the specific gravity of the wood at that moisture content. That is when sg(12%) is most commonly used.)

Basic specific gravity, sg(basic) or sg(green), is estimated by comparison of the wood's mass at 0% to its volume when green (30% MC or above.) Basic specific gravity is not given in most online reference pages, but they can be found for many species around the world in Tables 5-3, 5-4, and 5-5 of the 2010 Wood Handbook. (The basic specific gravity is identified by that at "green" moisture content in the tables, as opposed to the specific gravities listed at 12% moisture content.) Other good sources for basic specific gravity are the IWCS "Useful Woods of the World" books, and online at The Wood Database. The most comprehensive tables of specific gravities, both basic and at 12%, for North American woods that I know of is compiled in "Specific Gravity and Other Properties of Wood and Bark for 156 Tree Species in North America", by Patrick Miles and Brad Smith. This book is available free online.

To get on with the calculation of green weight...by the magic of algebra, we transform Equation 1 above to

m_green = m_dry * (1 + MC) (2)

Recall that m_dry is the mass of dry wood and MC is the moisture content at which we wish to estimate the weight. We will use the mass of one cubic meter for m_dry, and for MC we have a choice: we could plug in an assumed moisture content, one taken from a green sample, or one taken from reference. There are not many references on the green weight of wood; for this exercise, I have used Table 4-1 of the 2010 Wood Handbook, which gives green weight of heartwood and sapwood for 40 North American hardwoods and 28 North American softwoods.

Let's take the oaks and hickories first. Table 4-1 list 12 species of oaks and hickories, and they average 59 in basic specific gravity. Recall that specific gravity is density in grams per cubic centimeter (g/cm³); since the denominator of the specific density is one cubic centimeter, and assuming we want to calculate the weight of a cubic meter, we simply have to multiply 0.59 * 1000 to get 590 kilograms as the m_dry for Equation 2.

Next, we need to know what moisture content to expect for the species in question when green. We could then refer again to our Table 4-1 of the 2010 Wood Handbook, and calculate that the average moisture content (heartwood and sapwood) for all 12 is 71%. Now we have all we need. The calculation becomes:

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

However, we know that with all the estimating and assuming we've been doing in these calculations, our point estimate of 63 pounds per cubic foot is too precise. A better way to state our expected green weight of oaks and hickories would be to use estimates based on variation around our mean estimates. To keep it simple, I calculate a Low Range estimate and a High Range estimate for moisture content as 1/3 and 2/3 of the way between the stated values of heartwood and sapwood moisture content. Having done that, we find that the lowest low range estimate is for sand hickory, at 56%, and the highest high range estimate is 85% for water hickory. Substituting these values for the grand average MC used above, and using the specific gravities for the species from which we get the MC range values, we get:

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

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

So a correct statement in the original article should have been that oaks and hickories average between 60 and 70 pounds per cubic foot green. If you only have one estimate of green moisture content to work with, simply use that number for the MC in the equation, as I do in the next example.

The next species we consider here is live oak, Quercus virginiana. Its basic density is 0.80. If we use 80% as the moisture content again (it isn't listed on the Wood Handbook table 4-1), our estimate of live oak's green weight is:

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

But we immediately notice that this estimate is pretty close to our previous calculation of the maximum theoretical weight of wood. What's wrong?

What we find is that there is a functional relationship between the specific gravity of a wood and the moisture content it can attain; in other words, at a certain point, the density of the wood limits how much moisture it can take in. Again a table from the 2010 Wood Handbook is helpful. Tables 4-6a and 4-6b give us the relationship between density of wood and moisture content. Unfortunately, the tables only go up to a specific gravity of 0.7, where the highest possible moisture content is listed as 72%. However, by extrapolating the table by the trend rate, we conclude that the highest possible moisture content of wood with a specific gravity of 0.8 to be 52%.

So, our better estimate of the weight of green live oak becomes:

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

This technique works well for all wood species.

For those of you who just can't get enough of this sort of thing, I've developed an Excel spreadsheet that calculates dry and green wood weight of different species from specific gravity and moisture content data from the various tables I've alluded to in this article. Also, if you have green moisture content data on species outside of North America, and you feel like sharing that data, please send it on and I will add those species with the appropriate calculations to the spreadsheet.

Reference

Wood: Its Structure and Properties. Volume 1. Edited by F.F. Wangaard. 1981. The Pennsylvania State University Press. Page 199.

Wood Handbook: Wood as an Engineering Material. 2010 Edition. The Forest Products Society.

Green Wood Weight Calculator

Download the excel spreadsheet to run your own calculations.

Hardwoods

Genus	Species	Common Name	Basic SG	SG @ 12%	% Moisture Content* Heartwood	% Moisture Content* Sapwood	% Moisture Content* Average	% Moisture Content* Range Low	% Moisture Content* Range High	Weight, one cubic meter (kg) 12% MC	Weight, one cubic meter (kg) Average Green	Weight, one cubic meter (kg) Low Green	Weight, one cubic meter (kg) High Green	Weight, one cubic foot (lbs) 12% MC	Weight, one cubic foot (lbs) Average Green	Weight, one cubic foot (lbs) Low Green	Weight, one cubic foot (lbs) High Green
Acer	saccharinum	Maple, Silver	0.44	0.47	58	97	78	71	84	470	781	752	810	29	49	47	51
Acer	saccharum	Maple, Sugar	0.56	0.63	65	72	69	67	70	630	944	937	950	39	59	58	59
Betula	papyrifera	Birch, Paper	0.48	0.55	89	72	81	78	83	550	866	853	880	34	54	53	55
Betula	lenta	Birch, Sweet	0.6	0.65	75	70	73	72	73	650	1035	1030	1040	41	65	64	65
Betula	alleghaniensis	Birch, Yellow	0.55	0.62	74	72	73	73	73	620	952	950	953	39	59	59	60
Carya	cordiformis	Hickory, Bitternut	0.6	0.66	80	54	67	63	71	660	1002	976	1028	41	63	61	64
Carya	tomentosa	Hickory, Mockernut	0.64	0.72	70	52	61	58	64	720	1030	1011	1050	45	64	63	66
Carya	glabra	Hickory, Pignut	0.66	0.75	71	49	60	56	64	750	1056	1032	1080	47	66	64	67
Carya	ovalis	Hickory, Red	0.62	0.68	69	52	61	58	63	680	995	978	1013	42	62	61	63
Carya	pallida	Hickory, Sand	0.62	0.68	68	50	59	56	62	680	986	967	1004	42	62	60	63
Carya	aquatica	Hickory, Water	0.61	0.62	97	62	80	74	85	620	1095	1059	1131	39	68	66	71
Celtis	occidentalis	Hackberry	0.49	0.53	61	65	63	62	64	530	799	795	802	33	50	50	50
Fagus	grandifolia	Beech, American	0.56	0.64	55	72	64	61	66	640	916	900	931	40	57	56	58
Fraxinus	americana	Ash, White	0.55	0.6	46	44	45	45	45	600	798	796	799	37	50	50	50
Juglans	nigra	Walnut, Black	0.51	0.55	90	73	82	79	84	550	926	911	940	34	58	57	59
Liquidambar	styraciflua	Sweetgum	0.46	0.52	79	137	108	98	118	520	957	912	1001	32	60	57	63
Liriodendron	tulipifera	Yellow-poplar	0.4	0.42	83	106	95	91	98	420	778	763	793	26	49	48	50
Magnolia	grandiflora	Magnolia, Southern	0.46	0.5	80	104	92	88	96	500	883	865	902	31	55	54	56
Malus	sylvestris	Apple	0.61	0.67	81	74	78	76	79	670	1083	1076	1090	42	68	67	68
Nyssa	sylvatica	Tupelo, Black	0.46	0.5	87	115	101	96	106	500	925	903	946	31	58	56	59
Nyssa	biflora	Tupelo, Swamp	0.46	0.5	101	108	105	103	106	500	941	935	946	31	59	58	59
Nyssa	aquatica	Tupelo, Water	0.46	0.5	150	116	133	127	139	500	1072	1046	1098	31	67	65	69
Platanus	occidentalis	Sycamore, American	0.46	0.49	114	130	122	119	125	490	1021	1009	1033	31	64	63	65
Populus	tremuloides	Aspen, Quaking	0.35	0.38	95	113	104	101	107	380	714	704	725	24	45	44	45
Populus	deltoides	Cottonwood, Eastern	0.37	0.4	162	146	154	151	157	400	940	930	950	25	59	58	59
Quercus	kelloggii	Oak, California Black	0.56	0.61	76	75	76	75	76	610	983	982	984	38	61	61	61
Quercus	rubra	Oak, Northern Red	0.56	0.63	80	69	75	73	76	630	977	967	987	39	61	60	62
Quercus	falcata	Oak, Southern Red	0.52	0.59	83	75	79	78	80	590	931	924	938	37	58	58	59
Quercus	nigra	Oak, Water	0.56	0.63	81	81	81	81	81	630	1014	1014	1014	39	63	63	63
Quercus	alba	Oak, White	0.6	0.68	64	78	71	69	73	680	1026	1012	1040	42	64	63	65
Quercus	phellos	Oak, Willow	0.56	0.69	82	74	78	77	79	690	997	989	1004	43	62	62	63
Tilia	americana	Basswood, American	0.32	0.37	81	133	107	98	116	370	662	635	690	23	41	40	43
Ulmus	americana	Elm, American	0.46	0.5	95	92	94	93	94	500	890	888	892	31	56	55	56
Ulmus	crassifolia	Elm, Cedar	0.59	0.64	66	61	64	63	64	640	965	960	970	40	60	60	61
Ulmus	thomasii	Elm, Rock	0.57	0.63	44	57	51	48	53	630	858	846	870	39	54	53	54
		Average	0.52	0.58	81	83	82			577	937	923	951	36	58	58	59

Softwoods

Genus	Species	Common Name	Basic SG	SG @ 12%	% Moisture Content* Heartwood	% Moisture Content* Sapwood	% Moisture Content* Average	% Moisture Content* Range Low	% Moisture Content* Range High	Weight, one cubic meter (kg) 12% MC	Weight, one cubic meter (kg) Average Green	Weight, one cubic meter (kg) Low Green	Weight, one cubic meter (kg) High Green	Weight, one cubic foot (lbs) 12% MC	Weight, one cubic foot (lbs) Average Green	Weight, one cubic foot (lbs) Low Green	Weight, one cubic foot (lbs) High Green
Abies	balsamii	Fir, Balsam	0.33	0.35	88	173	131	116	145	350	761	714	807	22	47	45	50
Abies	grandis	Fir, Grand	0.35	0.37	91	136	114	106	121	370	747	721	774	23	47	45	48
Abies	procera	Fir, Noble	0.37	0.39	34	115	75	61	88	390	646	596	696	24	40	37	43
Abies	amabilis	Fir, Pacific Silver	0.4	0.43	55	164	110	91	128	430	838	765	911	27	52	48	57
Abies	concolor	Fir, White	0.37	0.39	98	160	129	119	139	390	847	809	886	24	53	51	55
Calocedrus	decurrens	Cedar, Incense	0.35	0.37	40	213	127	98	155	370	793	692	894	23	49	43	56
Chamaecyparis	lawsoniana	Cedar, Port Orford	0.39	0.43	50	98	74	66	82	430	679	647	710	27	42	40	44
Cupressus	nootkatensis	Cedar, Yellow	0.42	0.44	32	166	99	77	121	440	836	742	930	27	52	46	58
Juniperus	virginiana	Cedar, Eastern red	0.44	0.47	37	115	76	63	89	470	774	717	832	29	48	45	52
Larix	occidentalis	Larch, Western	0.48	0.52	54	119	87	76	97	520	895	843	947	32	56	53	59
Picea	mariana	Spruce, Black	0.41	0.42	52	113	83	72	93	420	748	707	790	26	47	44	49
Picea	engelmannii	Spruce, Engelmann	0.33	0.35	51	173	112	92	132	350	700	633	767	22	44	39	48
Picea	sitchensis	Spruce, Sitka	0.37	0.4	41	142	92	75	108	400	709	646	771	25	44	40	48
Pinus	strobus	Pine, Eastern White	0.34	0.35	98	219	159	138	179	350	879	810	947	22	55	51	59
Pinus	taeda	Pine, Loblolly	0.47	0.51	33	110	72	59	84	510	806	746	866	32	50	47	54
Pinus	contorta	Pine, Lodgepole	0.38	0.41	41	120	81	67	94	410	686	636	736	26	43	40	46
Pinus	palustris	Pine, Longleaf	0.54	0.59	31	106	69	56	81	590	910	842	977	37	57	53	61
Pinus	ponderosa	Pine, Ponderosa	0.38	0.4	40	148	94	76	112	400	737	669	806	25	46	42	50
Pinus	resinosa	Pine, Red	0.41	0.46	32	134	83	66	100	460	750	681	820	29	47	42	51
Pinus	echinata	Pine, Shortleaf	0.47	0.51	32	122	77	62	92	510	832	761	902	32	52	48	56
Pinus	lambertiana	Pine, Sugar	0.34	0.36	98	219	159	138	179	360	879	810	947	22	55	51	59
Pinus	monticola	Pine, Western White	0.36	0.48	62	148	105	91	119	480	738	686	790	30	46	43	49
Pseudotsuga	menziesii	Douglas-fir, Coastal	0.45	0.48	37	115	76	63	89	480	792	734	851	30	49	46	53
Sequoia	sempervirens	Redwood, Old Growth	0.38	0.4	86	210	148	127	169	400	942	864	1021	25	59	54	64
Taxodium	distichum	Baldcypress	0.42	0.46	121	171	146	138	154	460	1033	998	1068	29	65	62	67
Thuja	plicata	Cedar, Western Red	0.31	0.32	58	249	154	122	185	320	786	687	885	20	49	43	55
Tsuga	canadensis	Hemlock, Eastern	0.38	0.4	97	119	108	104	112	400	790	776	804	25	49	48	50
Tsuga	heterophylla	Hemlock, Western	0.42	0.45	85	170	128	113	142	450	956	896	1015	28	60	56	63
		Average	0.40	0.43	60	152	106			425	803	744	862	27	50	46	54