by Todd Walker
Ever wonder about the height of a tree on a nature walk? Or how far you’d have to climb to summit a rock face? Curiosity may be the only reason you’d ever need to know or use these techniques mentioned below.
Without being overly dramatic, accurate estimations could save you in the outdoors. Take campsite selection, for instance. You find what seems to be a perfect spot to camp. Water and firewood are close at hand. There’s even a fire pit with a bit of wood laid up from previous campers. Being smart, you look up to scan the horizon before dropping your pack. You’re scouting for the 4 W’s. You spot in the distance a very tall, very dead tree. How tall? And could it reach your campsite if it fell?
Do a quick estimate on the height so you can sleep without worry of that tree crashing through your tent.
Here are 4 accurate ways to estimate the height of trees and other structures if you don’t have a compass. By the way, always carry a quality compass!
This is the easiest method with no math calculations involved. Grab a small stick or twig. Ax handles work, too.
Put some distance between you and the tree or object. Facing the tree, hold a stick/twig vertically so that a 90º angle is formed between your outstretched arm. Align the tip of the stick with the top of the tree. Move your hand up or down on the bottom of the stick until your thumb aligns with the base of the tree while the tip is in line with the treetop.
Now rotate the stick ninety degrees clockwise, for the left-handers, or counterclockwise if the stick is in the right hand. Be sure to keep your thumb on the pivot point (origin) – base of the tree. Make a note of where the tip of the stick appears to touch the ground. If you have a partner, they can stand and mark the spot with your directions. The distance from this spot back to the base of the tree is the approximate height of the tree.
This is an easy method to determine the path of a tree you want to fell in your yard or camp. Check out the video of two of these methods in the woods…
Knowing the height of a cliff could help you decide whether to climb the obstacle or not. Place an object of known height at the base of the cliff. This object could be a person or walking staff. Stand back away from the rock face. Hold a small stick, as described in the Lumberjack technique above, so that the tip is aligned to the top of the person or walking staff and your thumb is sighted on the base of the known object.
Move this known unit of measure, thumb to tip of stick, up the cliff face to give you an estimate of its height. Let’s say your obstacle measures 4 units. Multiply the height of your known object (person or walking staff) times 4 to determine the height of the cliff. [Ex: 6′ x 4 units = 24 feet]
Use Your Shadow
On a sunny day, a tree casts a shadow. The shadow on the ground is one side of a right triangle. The distance from the top of the tree to the end of the shadow is the hypotenuse. The tree forms the third side of the right triangle.
Remember how we used Pythagorean Theorem (right triangles) to determine distance? Well, we’re using two right triangles again. This time we are using two triangles of different size yet proportional.
Here’s how it works and what you’ll need…
Measure the distance of the tree’s shadow. Now place an object of known height (yourself or walking stick) in the sun. Observe where this shadow ends and measure the distance or length of the shadow.
Now we have three measurements:
- Tree shadow
- Your shadow
- Your height
What we want and need is the missing measurement – the height of the tree “x”.
Set up a proportion using the corresponding sides of each triangle as illustrated in the diagram above. Be sure to place the corresponding sides across from each other. For instance, the shadow lengths are the numerators (top numbers) and the height measurements are both denominators (bottom numbers). You can flip-flop these numbers as long as the sides correspond to each other.
Cross multiply and divide to find the missing length. In the example given, the height is 24 feet. If you do your math right, this is a very accurate method.
Eleven + 1 Method
Here’s another accurate way to determine height which only requires a stick.
From the base of the tree, measure 11 equal units straight away from the tree. The key to using this method accurately is to make the 11 units about the same distance as the object you wish to measure. For instance, you may estimate that a tree appears to be about 30 feet tall. 30 divided by 11 gives you a rough estimate of about 3 feet per unit. One of my walking steps would work for my unit of measure. For a tree double that height, I would use two steps as my unit of measure.
Mark the spot of your 11 unit on the ground. Drive a straight stick in the ground so that it is vertical/plumb. Measure one more unit away from the stick and mark the spot.
Bend down to the ground with your dominate eye as close to the ground as possible at the 12th unit. Sight in the base of the tree to the bottom of the stick. Now look up the stick until your line of sight crosses the stick at the top of the tree. Mark this spot on the stick. The distance between these two points in inches equals the height of the tree in feet.
Your Body as a Measuring Device
It’s always helpful to know your personal measurements in the event you are without a measuring device. The most common way is to measure with steps.
Other personal measurements you should know are…
- Thumb to pinky finger (8 inches for me)
- Elbow to finger tip (19 inches)
- Arm pit to finger tip (28 inches)
- Height standing flat-footed with hand extended above head (88 inches)
- Finger tip to finger tip with arms spread forming a “t” (73 inches)
- Outside boot measurement (12.5 inches)
- Personal height (5′-10″)
Another clever way to know certain lengths is to know the length of your ax or other bushcraft equipment. The Plumb BSA Ax I carry is 26 inches long. Adding marks to the ax handle in one inch increments will also save time and calculations should the need arise. Don’t forget that Leatherman Multitools have both inch and centimeters marked on the side of these tools.
Each of these methods can be used without any special equipment. All you need is a stick and some basic math skills.
Keep Doing the Stuff of Self-Reliance,
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Another great (and infinitely useful!) post.