What this calculator does
Tree height comes from one angle and one distance. Stand a measured distance from the trunk, sight the top with a clinometer, and the height is the tangent of that angle multiplied by the distance, plus your eye height.
Eye height is the part that gets dropped and it should not be. The clinometer measures the rise above your eye, not above the ground, so the height from eye level to the top has to have your eye height added back on. On a 100 foot sighting at 35 degrees it is 5.5 feet out of 75.5, which is about 7% of the answer.
The formula
The angle to the treetop is converted to radians and its tangent multiplied by the horizontal distance, giving the rise from eye level to the top. Eye height is added to convert that into height above ground. The method assumes level ground and a vertical trunk, and the distance must be horizontal rather than measured along a slope.
| Term | Meaning |
|---|---|
| Clinometer | An instrument measuring the angle of elevation. Phone apps do the same job adequately for this purpose. |
| Angle of elevation | The angle above horizontal from your eye to the treetop. |
| Eye height | Ground to your eye, which must be added to the calculated rise. |
| Horizontal distance | Distance along the ground from you to the base of the trunk, not the slope distance. |
The inputs explained
| Field | What to enter |
|---|---|
| Distance from tree (ft) | Horizontal distance from you to the tree base. Around the same as the tree height gives the most accurate angle reading. |
| Angle to treetop β (°) | Angle of elevation to the top of the tree, in degrees. |
| Eye height (ft) | Your eye height above the ground, in the same units as the distance. |
When to use it
Measuring a tree before felling
Knowing the height determines whether there is room to drop it safely, which is the most common practical reason for the measurement.
Forestry inventory
Height paired with diameter at breast height gives volume estimates, and both are standard measurements in any stand assessment.
Checking a tree near a structure
Whether a tree can reach a building if it falls is a height question, and estimating by eye is notoriously unreliable.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How does the sighting angle change the height?
A fixed distance and eye height across a range of sighting angles.
| Angle to treetop | Tree height | Rise from eye level | Angle used |
|---|---|---|---|
| 20° | 41.9 ft | 36.4 ft | 20.0° |
| 35° | 75.5 ft | 70.0 ft | 35.0° |
| 50° | 124.7 ft | 119.2 ft | 50.0° |
| 65° | 220.0 ft | 214.5 ft | 65.0° |
Questions
How far from the tree should I stand?
Roughly the height of the tree, which puts the sighting angle near 45 degrees. Too close and the angle becomes steep, where the tangent changes rapidly and a small reading error becomes a large height error. Too far and the top becomes hard to sight clearly.
Do I need to add my eye height?
Yes, and forgetting to is the most common error. The clinometer measures the rise above your eye, so the calculation gives height above eye level. Your eye height has to be added to get height above ground.
What if the ground is sloping?
The simple method assumes level ground. On a slope, sight both the top and the base of the tree and combine the two angles, adding them if the base is below eye level and subtracting if above. The single-angle method will be wrong on any significant slope.
Can I use a phone instead of a clinometer?
Yes, phone inclinometer apps are accurate enough for most purposes. The larger error is usually in measuring the horizontal distance and in sighting the true top of the tree, which is often not the point that appears highest from where you are standing.
For trunk diameter from a circumference measurement, see the tree DBH calculator. For stand basal area, see the tree basal area calculator.