<P> Observing a nearby small object without a magnifying glass or a microscope , the size of the object depends on the viewing distance . Under normal lighting conditions ( light source ~ 1000 lumens at height 600 -- 700 mm , viewing angle ~ 35 degrees ) the angular size recognized by naked eye will be round 1 arc minute = 1 / 60 degrees = 0.0003 radians . At a viewing distance of 16 '' = ~ 400 mm , which is considered a normal reading distance in the USA , the smallest object resolution will be ~ 0.116 mm . For inspection purposes laboratories use a viewing distance of 200 -- 250 mm , which gives the smallest size of the object recognizable to the naked eye of ~ 0.058 - 0.072 mm ( ~ 55 - 75 micrometers ) . The accuracy of a measurement ranges from 0.1 to 0.3 mm and depends on the experience of the observer . The latter figure is the usual positional accuracy of faint details in maps and technical plans . </P>
what is the limit of resolution of the human eye in micrometers
~ 0.116 mm