Forestry Clinometer Tree Height Calculator
Enter the distance to the trunk, the top and base readings, and the clinometer scale. The calculator corrects slope distance, estimates a conservative height range, and can compute live crown ratio from a crown-base reading.
Estimated tree height74.53
- Conservative height range
- 71.47 to 77.64 ft
- Slope-corrected horizontal distance
- 99.03
- Height above eye-level plane
- 69.34
- Base offset from eye-level plane
- -5.19
- Live crown length
- 37.16
- Live crown ratio
- 49.86%
- Minimum suggested horizontal baseline
- 57.78
- Baseline and reading check
- OK for these entries.
Distances and heights are reported in ft.
How to use this calculator
- Measure to the trunk position directly below the sighted top, using either horizontal distance or taped slope distance.
- Choose degrees or percent slope to match the scale used on the clinometer.
- Enter signed readings to the top and base, with negative values below your horizontal sightline.
- Add the live-crown-base reading only when the lowest continuous live crown was sighted on the same scale.
- Enter realistic distance, reading, and slope uncertainties to see the conservative height range.
How the clinometer height is calculated
This calculator uses the tangent method used in ordinary forestry field work. The distance must be the horizontal distance from the observer to the vertical line through the sighted top. If the tape was pulled along sloping ground, the calculator first converts it with Dh = Dm * cos(phi), where Dm is the taped distance and phi is the ground slope angle. If the distance was measured horizontally, Dh = Dm.
Each clinometer reading is changed into a rise-to-run factor. For degree readings, F(r) = tan(r * pi / 180). For percent-slope readings, F(r) = r / 100. With top reading T and base reading B, total tree height is:
H = Dh * (F(T) - F(B))
The calculator also reports the two pieces of that height: Zt = Dh * F(T), the height above the observer's horizontal plane, and Zb = Dh * F(B), the signed base offset from that plane. A negative base offset means the base is below eye level; a positive value means the observer is below the base.
Live crown ratio and baseline choice
When a reading to the lowest live crown is entered, the height from the base to that point is Hc = Dh * (F(C) - F(B)). Live crown length is Lc = H - Hc, which is the same as Dh * (F(T) - F(C)). Live crown ratio is 100 * Lc / H. The crown-base reading must fall between the base and top readings; otherwise the crown result is suppressed because the sighted point is outside the measured tree height.
The baseline recommendation reverses the same geometry. A 120% slope reading is a 1.20 rise-to-run ratio, so the suggested horizontal distance is D120 = max(abs(Zt), abs(Zb)) / 1.20. Standing at least that far away keeps the top and base sights inside a practical clinometer range for the same vertical offsets.
Uncertainty and limits
The conservative range evaluates the height formula at the low and high endpoints of the entered distance uncertainty, top-reading uncertainty, base-reading uncertainty, and, when needed, ground-slope uncertainty. The smallest and largest valid heights become the reported interval. With zero uncertainty, both ends of the interval equal the main estimate.
The estimate moves most with horizontal distance and with steep top or base readings. Readings near vertical are especially sensitive, so degree-mode readings must stay strictly between -90 and 90 degrees. Percent readings above 120% are still computable, but they are flagged because small field errors can move the height a lot.
What this calculator leaves out
The tangent method estimates vertical height above the tree base. It does not measure trunk length along a leaning or curved stem, and it assumes the distance reaches the vertical projection of the sighted top. Crown selection, hidden tops, instrument calibration, visibility, and tree lean are not included in the uncertainty range.
Worked example
Suppose a forester tapes 100 ft along ground sloping 8 degrees and reads 35 degrees to the top and -3 degrees to the base. The horizontal distance is 100 * cos(8 degrees) = 99.03 ft. The height is 99.03 * (tan(35 degrees) - tan(-3 degrees)) = 74.53 ft.
If the lowest live crown is read at 18 degrees, the live crown length is 99.03 * (tan(35 degrees) - tan(18 degrees)) = 37.16 ft, and live crown ratio is about 49.86%. With distance uncertainty of 1 ft, reading uncertainty of 0.5 degrees, and slope uncertainty of 1 degree, the conservative height range is about 71.47 to 77.64 ft.
Common questions
Should distance to a tree be measured horizontally or along the ground?
Horizontal distance is the quantity used in the tangent height formula. If you measured along sloping ground, enter that as slope distance and include the ground slope angle so the calculator can apply the cosine correction.
How do I enter a negative clinometer reading?
Use a negative value when the point you sight is below your horizontal eye-level line. A common case is standing uphill from the tree base, where the base reading is negative and the top reading is positive.
How do percent-slope and degree clinometer scales differ?
A degree scale reports the sight angle, so the calculator uses the tangent of that angle. A percent-slope scale already reports rise divided by run times 100, so a 35% reading is entered as 35 and becomes a factor of 0.35.
Why do I need readings to both the top and the base?
The base is not always at the observer's eye-level plane. Subtracting the base reading accounts for standing uphill or downhill from the tree and for trees whose base is above or below the instrument.
What does a clinometer reading over 120% mean?
A 120% slope reading means 1.2 units of rise for each unit of horizontal distance. Readings beyond that are geometrically valid on a percent scale, but field accuracy is usually poor because a small aiming or distance error creates a large height change.
What is live crown ratio and how is it measured?
Live crown ratio is the live crown length divided by total tree height, expressed as a percent. Sight the lowest continuous live crown with the same scale used for the top and base; the point must fall between the base and top readings.