The most accurate way to measure something is using a tape measure, but some things are too tall (or too scary) to climb with a ruler. Try the different methods for the same tree and see how similar (or different) the results are. These examples are all about trees, but would work for buildings, telegraph poles and any other tall structures.
Get an adult to walk away from a tree until they are just about able to see the top of the tree when they bend over and look through their legs. The distance they are from the tree is roughly the same as the height of the tree.
This works because an adult bending over and looking up at the top of the tree creates about a 45 degree angle. This creates a triangle where the base and the height are about equal – so the distance from the tree is about the same as the height of the tree.
On a sunny day, measure the length of a tree’s shadow. Measure the length of the shadow of something of a known height (for example a person, a measuring stick or a pole). Divide the length of the tree’s shadow by the length of the person, measuring stick or pole’s shadow and then multiply it by the height of the person, measuring stick or pole – the answer is the height of the tree.
Using Shadows #2
Stick a long stick in the ground (one or two metres tall if possible), and draw a circle around the base of it, so that the distance from the centre to the circle is exactly the same as the distance from the ground to the tip of the stick. When the tip of the shadow touches the edge of the circle, the length of the shadow is exactly the same as the height of the stick. Run to the tree and measure the length of the shadow – this will be the height of the tree.
Using a Camera
Set up a digital camera on a tripod and get someone to stand next to a tree holding a measuring stick or a stiff tape measure, extended as far as possible (one to two metres long if available). Take a picture of the person and tree, with the tree taking up about half the height of the picture.
On a computer, use the manipulation tool to copy a rectangle exactly the same height as the measuring tape or stick and paste it a number of times up the side of the tree and see how many times the measuring stick or tape needs to be pasted to measure the height of the tree. Multiply this number by the height of the measuring stick or tape measure to get the height of the tree.
Using a Stick
Choose a stick that is exactly the same length as the distance from fingertips (arm fully stretched out) to eye. Hold the stick vertically (arm at full stretch) and walk away from the tree until the tree height is the same as the stick. Measure the distance to the tree – this is its height.
Tracking Tree Growth
People working in forestry use clinometers or theodolites to measure slopes and angles, and use these to calculate the height of a tree.
Keep a record of tree heights over a year – how quickly do they grow? Do different kinds of trees grow at different rates? Try measuring the girth (the distance around the trunk) as well – be careful not to damage the bark.