Here's something from high school geometry that I've actually used. Go out mid-morning or mid-afternoon on a sunny day, and measure the length of the tree's shadow. Then measure the length of the shadow of something short enough to measure readily, like a post or a person. The ratio of the length of the shadow of the known object to its actual height will be the same as of the tree's shadow to its height. A simple calculation will give you the height of the tree. It goes something like this: Hk = Known Object Height Sk = Length of Known Object's Shadow Ht = Tree's Height (Intitially unknown, to be solved for) St = Length of Tree's Shadow Hk/Sk = Ht/St so St(Hk/Sk) = Ht This works whether the shadow is longer or shorter than the object. If can hit the time of day when the shadow is the same length as the object, there's not even a calculation to make. If the tree is situated so you can't measure its shadow well, it will be necessary to do this the harder way. At some distance horizontal from the base of the tree, determine the angle from horizontal of the line of sight to to the top. Trigonometry will allow you to solve for the dimensions of the right triangle you have just formed, with the tree as the opposite side, and the distance from the tree as the adjacent side. So if the angle is Q, distance from the tree is D, and the height of the tree is H, then, (tangent(Q))D = H

An easy but crude way of estimating the height of a tree is through comparison. You can use a friend of known height to stand next to the tree. To keep this simple, say your friend is 5 ft. tall. Simply estimate how many times your friend would have to be duplicated to match the height of the tree. You can be creative and use a finger or pencil to duplicate the height of your friend and then just visually count up the number of times it must be duplicated to match the trees height. The larger the tree and the shorter your friend, the more inaccuracy in this method.

This is also a crude but moderately effective way to measure the height of a tree or any tall object that I learned in the Boy Scouts. Seems like a long time ago. . Stand rather far back from the object in question. Have a straight stick of any kind in your hand. Hold the stick at arms length so that you can just see the top of the tree at the top of the stick. Place your hand on the stick so that it is where you see the base of the tree and the top of the tree with your arm still extended. Now, keeping your line of sight so that your hand remains lined up with the bottom of the tree turn your stick hand 45 degrees so that you are sighting the top of the stick at a point on the ground. Have a friend go to that point, or use some reference to identify that point. The distance from that point to the base of the tree is the same as the height of the tree. Easy to do, hard to describe.