Estimating Standing Tree Volume

This is part one of a two part blog series: Estimating Volume and Value of Standing Timber

Due to the natural contour, shape and the individual characteristics of tree growth, scaling standing timber and assessing the value of a stand of timber can seem like a daunting task.

Although there is no substitute for the expert eye that can only develop from years of practice, the process is not as mystical as many loggers would lead you to believe. With a little knowledge and some simple tools, you can get a relatively close estimate of a standing trees volume. From the volume, you can get a decent idea of the range of values this tree may be worth.

When determining board footage, you are estimating the amount of lumber that can be cut from a particular tree, not the amount of wood the tree contains. For the purposes of this blog, we will be explicitly dealing with lumber volume, which represents a very high proportion of a trees total value—determining the volumes of cordwood and pulpwood that can be cut from a particular tree is a lesson for another day. In the second installment of this blog series we will show you how to take the volume estimates we determine today and use widely available forestry data to get an idea of what your timber is worth.

First Measure Tree Diameter

DBH is defined as the diameter of the tree taken 4.5 feet up the trunk on the uphill side.

The overwhelming standard for calculating the board footage (cubic measure equaling 144 square inches) is the Doyle Scale.

With a couple of measurements taken from the tree the Doyle Scale will give us the tree’s volume. The first number we need to use our scale is the diameter at breast height (DBH). DBH is defined as the diameter of the tree taken 4.5 feet up the trunk on the uphill side. Diameter is taken this far up to account for the various degrees to which trees will flare at the at their base.

Don’t worry if it’s been a few years since your high school geometry course—it is common to confuse diameter (the measure across the tree equal to twice its radius) with circumference (the measure around a tree). When someone says they have a tree that is 5 or more feet in diameter, they likely are actually referring to circumference.

Because it is impossible to stick a ruler through a standing tree, the number you come up with won’t perfect. Just do your best to estimate the distance between the bark on one side to the other. In fact, the tables we’ll use in the next step only contain entries for trees at even inch markers—16 inches, 18, 20, etc.—so take your DBH measurement and round to the nearest even number. A tree that measures 18.9 inches will round down to 18 inches. A 19.6 inch tree rounds up to 20.

Next Estimate Tree Height

After we have the diameter of the tree we need to estimate it’s height. We’re not interested in the overall tree height—just the point at which the trunk narrows to 8 inches or where the tree contains too many defects—large limbs, knots, hollow spots, etc.—to be commercially valuable. Tree lengths are reported in 16 foot lengths, so a tree that is 32 feet tall would have two 16 foot sections.

While you get to be pretty good at estimating this height by sight—remember you’re really only trying to guess to the nearest 8’—there are a number of tools to help you get this right. The most commonly used tool for this purpose is a Biltmore stick, easily available and quite affordable online.

Biltmore sticks are calibrated to be read either 66 or 100 feet away and have markings along the stick that correspond to tree heights. Held 25″ from your face, align the bottom of the stick with the bottom of the tree and adjust your line of sight (without moving your head) to read how many 16 foot sections are in the tree. When determining tree height you always round down to the closest whole or half stick. In other words if your Biltmore stick tells you that a particular tree is very close to 3 logs, you must scale it as 2.5 16 foot sticks, not 3.

Once you’ve determined the height of your tree you just plug the two numbers into the Doyle Scale.

The Doyle Scale

Use the table below to calculate the board footage contained in your standing timber. DBH numbers run down the left column while the number of 16 foot sticks runs across the top. Board footage figured are listed in the middle of the table at the intersections of the two numbers you learned how to calculate above.

D.B.H.	No. of 16 Foot Sticks
	1/2	1	1-1/2	2	2-1/2	3	3-1/2
10 inches	21	34	44	55
12 inches	30	52	68	85	98
14 inches	42	74	99	124	143	162
16 inches	59	100	134	169	198	226	246
18 inches	74	129	175	221	259	297	325
20 inches	92	162	220	279	328	377	413
22 inches	112	198	271	344	406	467	514
24 inches	133	237	326	415	491	567	622
26 inches	158	284	392	500	592	684	755
28 inches	187	331	458	585	696	806	888
30 inches	220	381	529	677	805	933	1029
32 inches	254	435	606	776	926	1077	1192
34 inches	291	493	687	881	1054	1227	1359
36 inches	333	559	782	1006	1205	1404	1557
38 inches	374	624	874	1125	1354	1582	1754
40 inches	415	693	974	1256	1510	1764	1962

In the next blog you’ll learn how to take data collected by your state forestry agency and estimate what you might be able to expect from selling your timber.