Here at webvideoproduction we are always writing or supervising short scripts for videos. When writing or supervising a script we are aware that we have to fit all the target content into a set time frame. Our average video durations are between 30 to 120 seconds long, so when writing the script it is critical that we keep within the a certain word count. The general rule of thumb is 150-170 words per minute. Speech delivered at this pace  produces what we consider to be theoptimum listening speed. Thus our recommended breakdown is as follows;

30 seconds = 75 words
45 seconds = 112 words
60 seconds = 150 words
90 seconds = 225 words
120 seconds = 330 words