The reading speed
of the “average” viewers (aged between 14-65, from an upper-middle socio-
educational class) for a text of average complexity (a combination of formal
and informal language) has been proven to range between 150-180 words per
minute, i.e. between 2 1/2-3 words per second. This means that a full two line
subtitle containing 14-16 words should remain on the screen for a maximum
time of something less than 5 1/2 seconds. However, we would actually have to
expand the estimate to around 6 seconds because one should also add about 1/4-
1/2 of a second that the brain needs to start processing the subtitle it has traced.
It should be noted that equal to the importance of retaining a full two-line
subtitle for at least 6 seconds to secure ample reading time, is the importance of
keeping the same subtitle not more than 6 seconds because this would cause
automatic re-reading of the subtitle, especially by fast readers.