Tree Height Calculator

Background.

Almost every quick way of measuring a tree gets the same thing wrong, and it is worth naming before anything else: they give you the height above your own eye, not the height of the tree. Point a phone inclinometer at the top of a tree from 100 feet away, read 38.7 degrees, and the trigonometry says 80 feet. The tree is 86. The missing six feet is the distance from your eye down to the ground at the trunk, and no single triangle can see it.

Every published field method solves this the same way: two sightings, not one. You read up to the top and then down to the base, and the reading to the base is negative because the base is below your eye. Subtracting a negative adds the missing piece back. The USDA Forest Service's research note on tree height measurement states the convention explicitly — the angle to the base is negative when the base is below the observer's eye level, so subtracting it produces a positive height component. Alabama Cooperative Extension teaches the same arithmetic to landowners as (distance divided by 100) times the sum of the two percent readings. This calculator reproduces every worked example in that chapter exactly, and reports the above-eye and below-eye parts separately so you can see how much the correction is worth on your tree.

Three methods are offered because they need three different amounts of equipment. The tangent method wants a clinometer or a phone inclinometer plus a tape, and it is the standard forestry approach. The sine method wants a laser rangefinder: instead of an angle and a baseline, you measure the straight-line distance to the top and to the base and take the sine of each angle. That sounds like a small change and it is not. Because it measures a real point in the crown rather than projecting a hypothetical one, the sine method is insensitive to lean, to ground slope, to crown width and to where you stand, and it cannot overestimate — which is why it has become the method for champion-tree certification. The shadow method needs nothing at all: on a sunny day the tree is to its shadow as you are to yours.

They are not equally accurate, and the note beside the result says which is which rather than leaving you to guess. The tangent method assumes the tree is vertical, that its highest point sits directly above the trunk, and that your baseline is a true horizontal distance. Real trees lean, spread and grow offset tips, and when they do the tangent method reads high. On sloping ground a taped distance is not a horizontal distance and must be corrected by multiplying by the cosine of the angle — this page does not do that for you, and says so.

The calculator also reports two forestry height classes, to the nearest 5 feet and the nearest 10 feet, using the Alabama Extension convention in which a height ending in 5 rounds down. A 66-foot tree is in the 65-foot class and the 70-foot class. These are inventory conventions rather than measurements, and they are always in feet regardless of the units you measured in.

One thing this page will not do is tell you whether a tree is safe. A lean, a cavity, a dead top or a root plate lifting after a storm are questions for a qualified arborist, and no amount of trigonometry substitutes for someone looking at the tree.

What is tree height calculator?

Total tree height is the vertical distance from the ground at the base of the trunk to the highest point of the crown. It is measured to the highest live or dead wood, not to the tip of the topmost leaves, and it is different from merchantable height (the usable stem up to a mill's diameter limit) and from height to live crown (the base of the canopy).

A clinometer is a hand-held instrument that reads the angle from horizontal to whatever you sight. Forestry clinometers carry two scales: a percent scale, which reads rise per hundred of run and is therefore already a tangent, and a topographic scale, which reads height directly when you stand a chain — 66 feet — from the tree. A phone inclinometer app is the same instrument with more error.

The tangent method computes height as the horizontal baseline times the difference of the two tangents, one to the top and one to the base. The sine method computes it as the slope distance to the top times the sine of its angle, minus the slope distance to the base times the sine of its angle. For a perfectly vertical tree the two give exactly the same answer, because the slope distance is the baseline divided by the cosine — and this calculator asserts that identity as a test. They diverge precisely when the tree is not vertical, and there it is the sine method that stays correct.

The shadow method is similar triangles. Two vertical objects lit by the same sun cast shadows in the same ratio, so the tree's height divided by the tree's shadow equals your height divided by your shadow. Similar-triangle hypsometers are the oldest indirect height instruments in forestry, going back to the rotary-mirror devices of the early 1900s.

Height classes are an inventory device, not a measurement. Rather than record every tree to the foot, cruisers assign each to a 5-foot or 10-foot class, so a 66-foot tree becomes a 65-class or 70-class tree depending on which granularity the cruise uses.

How to use this calculator.

1. 01Pick the method that matches what you have. Clinometer or phone plus tape: tangent. Laser rangefinder: sine. Nothing but sunshine: shadow.
2. 02Set the unit for every distance you will enter. The height comes back in that unit and is also converted to the other one.
3. 03For the tangent method, walk out until the horizontal distance to the trunk is at least the height you think the tree is, and measure it. On sloping ground, multiply a taped distance by the cosine of the angle to where you are holding the tape to get the true horizontal distance.
4. 04Sight the highest point of the crown and record the reading, then sight the base of the trunk at ground level and record that one too. Enter the base reading as a NEGATIVE number if the base is below your eye, which it usually is.
5. 05For the sine method, laser the straight-line distance to the top and to the base, and record the angle to each. You still enter the base angle as negative when the base is below your eye.
6. 06For the shadow method, measure the tree's shadow from the trunk to its tip, then immediately measure a vertical object of known height and its shadow. Do both within a minute or two, because the sun moves.
7. 07Read the split between above-eye and below-eye height beside the result. On a typical suburban sighting the below-eye piece is five or six feet, and that is the difference between this calculator and a plain triangle solver.
8. 08Read the method note before trusting the number, especially if the tree leans, spreads wide, or stands on a slope.

The formula.

The tangent method is height equals the horizontal baseline times the tangent of the angle to the top, minus the baseline times the tangent of the angle to the base. Because a clinometer's percent scale already reads a tangent — 80 per cent means 80 of rise per 100 of run — the arithmetic on a percent scale is even simpler: multiply the baseline by the sum of the two readings and divide by 100. From 100 feet with readings of plus 80 and minus 6, that is 100 divided by 100, times 86, which is 86 feet. Split it and the top of the tree is 100 times 0.80, or 80 feet above your eye, and the ground at the trunk is 100 times 0.06, or 6 feet below it. Alabama Extension prints exactly this example and exactly this answer.

The sine method replaces the baseline and the tangents with slope distances and sines: height equals the distance to the top times the sine of its angle, minus the distance to the base times the sine of its angle. For a vertical tree the two methods are algebraically identical, because the slope distance to a point is the baseline divided by the cosine of the angle, and dividing by cosine then multiplying by sine is multiplying by tangent. A 100-foot baseline with sightings of plus 40 and minus 5 degrees gives 92.658 829 470 3 feet either way, to ten decimal places. What breaks the identity is a tree that is not vertical, and there the sine method is right and the tangent method reads high.

The shadow method is a proportion: tree height equals reference height times the tree's shadow divided by the reference shadow. A six-foot person casting an eight-foot shadow beside a tree casting a ninety-foot shadow gives 6 times 90 divided by 8, which is 67.5 feet. The ratio of reference height to reference shadow is also the tangent of the sun's elevation, so the page reports that angle too — arctan of 6 over 8 is 36.87 degrees.

Units are converted at exactly 0.3048 metres per foot, the international foot definition, so 86 feet is 26.2128 metres. The two height classes always come out in feet, because they are a US forestry convention. The 5-foot class is 5 times the ceiling of the height minus 2.5, all over 5; the 10-foot class is 10 times the ceiling of the height minus 5, all over 10. Those offsets are what make a height ending in 5 round down, which is the published rule: trees between 62.6 and 67.5 feet are in the 65-foot class, and trees from 66 to 75 feet are in the 70-foot class. An 86-foot tree is therefore in the 85-foot class and the 90-foot class.

Everything is carried at forty significant digits and rounded once at the end, to ten decimal places, with pi computed rather than typed. The only intermediate rounding is the two ceilings that produce the height classes, and both are applied to the unrounded height in feet, so a tree measuring 67.500 000 1 feet lands in the 70-foot class and not the 65-foot one.

A worked example.

Frequently asked questions.

References& sources.

1. [1]Bragg, D.C.; Frelich, L.E.; Leverett, R.T.; Blozan, W.; Luthringer, D.J. 2011. "The sine method: an alternative height measurement technique." Research Note SRS-RN-22. Asheville, NC: U.S. Department of Agriculture, Forest Service, Southern Research Station. 12 p. Source of equation (2) (tangent method, with the explicit convention that the angle to the base is negative when the base is below the observer's eye level, so subtracting a negative produces a positive height component), equation (3) (slope-to-horizontal baseline correction) and equation (4) (sine method). Retrieved 2026-07-31; open access PDF, read in full.
2. [2]Alabama Cooperative Extension System (Auburn University), "Forest Inventory Basics for Family Forest Landowners", Chapter 8, "Measuring Tree Heights" (FOR-2082). Source of the percent-scale clinometer procedure, of the three worked examples and five answer-key results this calculator reproduces exactly, and of the 5-foot and 10-foot height class definitions — "trees measuring between 62.6 and 67.5 are in the 65-foot class" and "trees that are 66 to 75 feet tall are in the 70-foot height class ... heights that end in 5 round down". Used as the independent check on the Forest Service equations. Retrieved 2026-07-31; open access PDF, read in full.
3. [3]Bragg, D.C. 2014. "Accurately measuring the height of (real) forest trees." Journal of Forestry 112(1):51-54. doi:10.5849/jof.13-065. Names the similar triangles and tangent methods as the two approaches that have dominated tree height measurement, traces similar-triangle hypsometers to Tieman (1904), and documents that the tangent method overestimates on leaning stems and offset crowns. Source of the accuracy ordering stated beside the result. Retrieved 2026-07-31; open access PDF, read in full.
4. [4]USDA Natural Resources Conservation Service with Iowa State University NRI Grazing Land, "Measuring Tree Height using a Clinometer". Corroborating field procedure: the topographic scale is read directly at 66 feet and the percent scale at 100 feet, and the base reading is subtracted from the top reading. Confirms the sign convention independently of both Forest Service documents. Retrieved 2026-07-31; open access.