Measuring the height of a tree

If you have access to a protractor you can make a simple clinometer which measures the angle from your eye to the top and base of a tree.

Clinometers can be bought for around £150 and are very useful if you do a lot of tree height estimating.

If you have a laser surveying device you can find the height much more easily, but it also costs much more.

Finally, if you are a good climber and have a long tape measure you can climb the tree, measuring height as you go. However, this is the most dangerous option – and it’s no more accurate than the others so I don’t recommend it.

Below are four easy methods to use. At most, they require a tape measure and so they’re all cheap, but can be fun too.

Method 1:

  • Guess the height by comparing the tree with a nearby structure of known height.
  • Most two storey houses are around 8m tall.
  • A garage is usually around 4.5m if it’s got a pitched roof.
  • A single storey of a block of flats or offices is likely to be around 2.5-3m in height.
  • A double decker bus is not taller than 5m.
  • Lamp posts can be of varying heights, depending on the area they are intended to illuminate and the brightness they have to give out. Lamp posts by roadsides will not be less than 5m in height. Some will be 6m, some 7.5m or 9m on larger roads. There might be some that are even taller.

Method 2:

  • Get a stick which is the same length as the distance from the base of your thumb to your eye.
  • Hold the stick vertically at arm’s length.
  • Look at the tree and move forwards or backwards until the stick looks to be the same height as the tree.
  • Measure the distance from your feet to the centre of the base of the tree. This distance is the same as the height of the tree.

Method 3:

  • Stand a person of known height beside the tree.
  • Stand far enough away from the tree so that you can see its whole height.
  • Use a pencil or ruler to measure how tall the person beside the tree looks.

How many person-heights are needed to reach the top?

  • Multiply the number of person-heights by the real height of the person to find the height of the tree.

Method 4:

  • Measure 30m from the centre of the base of the tree with a tape measure.
  • One person lie down with their eyes at the point 30m from the tree.
  • Hold a straight stick vertically at 27m from the tree. The 3m from the stick to the eye is one tenth of the distance between the tree and the eye.
  • The person lying down must look at the stick and the tree.
  • The person holding the stick then marks the stick at the point which seems to the person lying down to be at the same height as the top of the tree.
  • The triangle now formed from the prostrate person’s eyes to the bottom of the stick, up to the mark on the stick and back to the lying person’s eyes is in the same proportion as the triangle from those eyes to the tree, to the tree top and back.
  • The height of the tree is, therefore, ten times the height of the point marked on the stick because the small triangle is ten times smaller than the large one.

Try the methods out and let me know how you get on.

Article written by Steve Cox on November 16, 2009