Calculate Width or Distance with the Thumb Method
Calculation of the width or distance of an object with the aid of the thumb. One value, distance or width, must be known or estimated. At eye distance and length of the stretched arm from eyes to thumb, average values are set. For a better estimation, you should take your measures.
Thumb method: stretch one arm and hold the thumb up. Then close the left eye and hold the thumb in front of the left border of the object (e.g. a house or a mountain). Now open the left and close the right eye. Remember the position behind the thumb. Change the eyes again and move the thumb to this position. Repeat, until you have reached the right border of the object with the left eye (this number doesn't need to be an integer, it can also be something like 0.5 or 2.3).
The formula for the calculation is: d = x * c * a / b
The specified values for eye distance and eyes-thumb distance are average values for normal-sized adults.
Example: A mountain 8 kilometers away is measured in three steps. At the preset distances, the mountain then has a width of approximately 2.4 kilometers.
The thumb method is a variation of the height estimation that requires no tools. With this method, also a height instead of a width can be estimated. To do this, you have to turn your head and thumb 90 degrees, or lie down. It is more convenient, but somewhat more prone to error, to measure a width that corresponds to the height to be measured.
Last updated on 07/01/2025. Author: Jürgen Kummer
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