How it works
Stand a measured level distance from the trunk and sight the top of the tree through the clinometer to get one angle, then sight the base to get a second. The tree, the level line from your eye, and each sight line form right triangles, so height above and below eye level are each the distance times the tangent of that angle.
A percent-scale clinometer reads the tangent times 100 directly, so a reading of 100% is 45°. Add the height above eye level to the depth of the base below it. On a slope where the base is above your eye, the base reading is positive and is subtracted.
Worked example
Standing 100 ft from a tree with a top reading of 38° and a base reading of −4° (base slightly below eye level):
- Height above eye level = 100 ft × tan(38°) = 78.1 ft
- Base relative to eye level = 100 ft × tan(-4°) = -7 ft (below eye level)
- Tree height = 78.1 − (-7) = 85.1 ft
| Input | Value |
|---|---|
| Horizontal distance to the trunk | 100 ft |
| Clinometer scale | Degrees |
| Reading to the top | 38 ° or % |
| Reading to the base | -4 ° or % |
| Result | Value |
|---|---|
| Tree height | 85.1 ft |
| Above eye level | 78.1 ft |
| Base below eye level | 7 ft |
Assumptions and limits
- The distance is measured horizontally to the trunk’s center line, on the same side you sight from.
- Leaning or crooked trees give less accurate results; stand where the lean is across your line of sight, not toward or away from you.
- The highest point you see is not always the top of the tree, especially in a dense crown. Move until the tip is clear.
Common questions
How far from the tree should I stand?
Far enough to see the top and base comfortably, about the tree’s height is common. The math works at any distance if the distance is measured level and the angles are read carefully.
What if the ground slopes?
Measure horizontal distance, and read the base angle separately. It will be negative when the base is below your eye level and positive when it is above.
What is percent scale?
A clinometer percent scale shows slope as rise per 100 of run, the tangent times 100. Height is then distance × reading ÷ 100.
Why is my answer different from a laser or a second reading?
Small angle errors grow with distance, and a leaning or hidden top adds error. Take readings from two sides and compare.
Sources
- Right-triangle trigonometry as used in forest mensuration for clinometer and hypsometer readings (e.g., Avery and Burkhart, Forest Measurements).
- Percent-scale clinometer readings are tan(angle) × 100 by definition.
Updated 2026-09-30