Tree Height Calculator
Measuring a tall tree without climbing it is possible using a simple geometric principle: similar triangles. On a sunny day, all vertical objects cast shadows at the same angle. This means the ratio of an object's height to its shadow length is constant for all objects measured at the same moment. If you know the height of a reference object (such as a person, a stake, or a fence post) and measure its shadow alongside the tree's shadow, you can calculate the tree height by cross-multiplying: tree height equals reference height multiplied by tree shadow length, divided by reference shadow length. This calculator does that arithmetic instantly. Enter the height of your reference object in feet, the length of its shadow in feet, and the length of the tree's shadow in feet. The result is the estimated tree height in both feet and metres. For the most accurate result, measure both shadows at exactly the same time (or as quickly as possible) on flat ground with both objects in full sun. A slightly overcast sky produces diffuse shadows that are harder to measure precisely. The note below the inputs explains the clinometer angle method as an alternative when shadows are not available.
Estimated tree height: -- ft (-- m)
Formula
Tree height (ft) = (reference height × tree shadow) ÷ reference shadow
= (6 × 20) ÷ 4 = 30.00 ft
How to measure using the shadow method: step by step
Step 1: Choose a reference object of known height. A 6-foot person is convenient; a measured stake or fence post of known height also works well.
Step 2: Go outside on a sunny day. The shadow method does not work on overcast days because there is no distinct shadow edge to measure.
Step 3: Stand the reference object upright next to the tree (or nearby on flat ground). Have a helper measure the length of the reference object's shadow from the base to the tip. Immediately measure the length of the tree's shadow from the base of the trunk to the tip of its shadow on the ground.
Step 4: Enter the three values into this calculator to get the estimated tree height.
Important: both shadows must be measured at the same time. The sun angle changes continuously, so even a few minutes between measurements can introduce noticeable error, especially when the sun is moving quickly near the horizon.
Alternative method: the clinometer (angle) approach
If shadows are not available (cloudy day, or a tree in a spot where the sun does not reach the ground), you can use the angle method instead. Stand at a measured distance from the base of the tree (for example 50 feet). Use a clinometer (a device or smartphone app that measures vertical angles) to sight the top of the tree and record the angle. Then:
Tree height = (distance from trunk) x tan(angle to top) + (your eye height above ground)
For example: standing 50 feet from the trunk, the angle to the top is 55 degrees, and your eye is 5.5 feet above the ground. Tree height = 50 x tan(55 deg) + 5.5 = 50 x 1.428 + 5.5 = 71.4 + 5.5 = approximately 77 feet. Free clinometer apps are available for iOS and Android smartphones.
Worked example
| Input | Value |
|---|---|
| Reference object height | 6.00 ft |
| Reference object shadow | 4.00 ft |
| Tree shadow length | 20.00 ft |
| Tree height (calculated) | (6 x 20) / 4 = 30.00 ft (9.14 m) |
Tree height calculator: frequently asked questions
How accurate is the shadow method for measuring tree height?
The shadow method is accurate when both the reference object and the tree shadow are measured at the same time, on flat ground, with both shadows cast in the same direction. In ideal conditions, accuracy is within a few percent. Errors arise if the ground is sloped, the sun angle changes between measurements (measure both shadows simultaneously or very quickly), or the shadows are not clearly defined (overcast conditions reduce precision).
What is the best time of day to measure tree shadows?
Mid-morning or mid-afternoon is ideal. The sun angle is high enough that shadows are clearly defined and not excessively long (very long shadows are harder to measure accurately), yet low enough that you get distinct shadows. Midday (near solar noon) works but may produce very short shadows that are harder to measure precisely. Avoid early morning or late afternoon when shadows become extremely long.
Can I use this method for buildings?
Yes. The shadow method works for any vertical object: trees, buildings, flagpoles, utility poles, or fences. Use a known-height reference object (a person of known height, a measured stake, or a fence post of known height) and measure both shadows at the same time. The formula is identical: tree (or building) height = (reference height x object shadow length) / reference shadow length.
What other methods can I use to estimate tree height?
The clinometer (angle) method uses a protractor or smartphone clinometer app to measure the angle to the top of the tree from a measured distance away. Height = distance x tan(angle). The stick method holds a stick equal in length to its distance from your eye, extends your arm, and uses similar triangles. Professional foresters use clinometers, hypsometers, and laser rangefinders for precise measurements. LiDAR technology on many modern smartphones can also estimate height.
Why would I need to know a tree's height?
Knowing a tree's height is useful before removing it (to ensure it will not hit structures when it falls), for planning clearance around power lines, for assessing whether a tree will block solar panels, for estimating timber volume, for matching plants to available vertical space, and for urban tree inventories. Arborists and surveyors measure trees regularly; the shadow method gives homeowners a quick non-specialist estimate.
References
- USDA Forest Service, "How to Measure Tree Height," forest management publications, fs.usda.gov
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. The shadow method gives an estimate only. Results depend on measurement accuracy and flat, uniform ground. For precise measurements (tree removal near structures, power lines), use a certified arborist. See our methodology.