The tangent method, and why eye height matters
Measure a straight-line distance to the trunk, sight the top, and read the elevation angle. Distance times the tangent of that angle gives the height above your eye. You then add your own eye height, because the angle is taken from eye level and misses the trunk below it. Leaving that term out is the usual mistake.
Angle drives everything — distance just scales it
The height above eye level is the distance multiplied by these factors. Read the multiplier for your angle, multiply by your distance, then add eye height.
| Angle to top | tan(angle) | Above eye at 20 m away |
|---|---|---|
| 30° | 0.58 | 11.5 m |
| 40° | 0.84 | 16.8 m |
| 45° | 1.00 | 20.0 m |
| 50° | 1.19 | 23.8 m |
| 60° | 1.73 | 34.6 m |
At 45° the tree above your eye equals your distance from it exactly, a handy pace-back trick: walk to where the top sits at 45°, and the height is that distance plus your eye height.
Picking a method for the conditions
- Shadows, no tools. Tree height = stick height × tree shadow ÷ stick shadow. Needs a sunny day and flat ground with sharp shadows.
- Clinometer or phone. Fast and accurate on level ground. A phone level app reads the angle to within a degree or two.
- Sloping ground. Sight the angle to both the top and the base and combine them, so the ground slope cancels out instead of skewing the height.
Common questions
How do you measure a tree with an angle?
Stand a measured distance from the trunk, sight the top through a clinometer or phone app, and read the angle. The height above your eye is the distance times the tangent of that angle. Add your eye height to get the full tree.
Why do you add eye height to the result?
The angle is measured from your eye, not the ground, so the tangent formula only gives the part of the tree above eye level. Adding your eye height, usually about 1.5 meters or 5 feet, accounts for the trunk below your line of sight.
How do I measure a tree height without any tools?
Use shadows. Stand a stick of known height upright and measure its shadow and the tree's shadow at the same time. The tree height equals the stick height times the tree shadow divided by the stick shadow.
How accurate is the angle method?
On flat ground with a careful reading it is within about 5 to 10 percent, or half a meter at 20 to 30 meters distance. Wind, sloping ground and a hard-to-see crown are the main sources of error.
