Measuring a tree without climbing it
You can find the height of a tree from the ground with two measurements: your horizontal distance from the trunk, and the angle up to the top. A clinometer, a phone app with an inclinometer or a simple protractor with a plumb line all work.
The two-angle method
Stand at a known distance, sight the very top of the tree and read the angle above horizontal. Then sight the base of the trunk and read that angle, which is negative if the base is below your eyes.
Height = distance × (tan top angle − tan base angle)
This works on slopes, because the base angle takes care of the difference in ground level.
The single-angle method
On flat ground you can sight only the top and add your eye height:
Height = distance × tan top angle + eye height
Example
Standing 66 ft from the trunk, the top is at 40° and the base at −5°:
- 66 × tan 40° ≈ 55.4 ft above eye level;
- 66 × tan 5° ≈ 5.8 ft below eye level;
- total height ≈ 61 ft.
Getting a good reading
- Stand back until the top is at 30° to 50°. Steep angles amplify small reading errors; very shallow angles are hard to read.
- Measure the distance with a tape or a laser rangefinder; pacing introduces large errors.
- On leaning trees, stand at right angles to the lean.
- On broad trees, the highest point may not be above the trunk; sight the real top, not a branch closer to you.
- Repeat from a second spot and average.
Low-tech alternatives
- The stick method: hold a stick at arm’s length, with its length equal to the distance from your eye to your hand. Walk back until the stick covers the tree from base to top; your distance from the trunk is then about the tree’s height (a 45° sighting).
- Shadows: on a sunny day, height of the tree = length of its shadow × your height ÷ length of your shadow.
Why measure tree height?
Height is used with trunk diameter to estimate timber volume, carbon storage and the age of a stand. It also tells you whether a tree could reach a house or a power line if it fell, which is useful before planning felling or pruning work. For hazardous trees, call a certified arborist.