Thumb's rule tested: visual angle of thumb's width is about 2 deg

Perception. 1991;20(3):415-8. doi: 10.1068/p200415.


Measures of the size of various hand parts and their viewing distance when held at arm's length were made on one hundred and eighteen undergraduate students. A simple rule of thumb can be confirmed: Visual angle of the width of the thumb held at arm's length is about 2 deg. The thumbnail subtends about 1.5 deg and the index fingernail about 1 deg in width, when both are held at arm's length. These figures are good approximations for males and females, although a significant, direct, linear relationship exists between hand-part size and the visual angle of the part at arm's length.

MeSH terms

  • Adult
  • Anthropometry
  • Distance Perception / physiology*
  • Female
  • Humans
  • Male
  • Orientation / physiology*
  • Psychophysics
  • Size Perception / physiology*
  • Thumb / anatomy & histology*