Thumb's Rule Tested: Visual Angle of Thumb's Width is about 2 Deg

• DOI: 10.1068/p200415
• Publication Date: 2007-01-23T15:29:17Z
• Authors: Robert P O'Shea
• Keywords: Adult; Male; Anthropometry; Distance Perception; 05 social sciences; 02 engineering and technology; Thumb; Orientation; Medicine and Health Sciences; Psychophysics; 0202 electrical engineering, electronic engineering, information engineering; Humans; Female; 0501 psychology and cognitive sciences; Size Perception

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.