The total capacity of short-term memory is fairly limited. Experts believe that you can hold approximately seven items in short-term memory for about 20 to 30 seconds. This capacity can be stretched somewhat by using memory strategies such as chunking, which involves grouping related information into smaller "chunks."
In a famous paper published in 1956, psychologist George Miller suggested that the capacity of short-term memory for storing a list of items was somewhere between five and nine. Today, many memory experts believe that the true capacity of short-term memory is probably closer to the number four.
See this in action for yourself by trying out this short-term memory experiment. Spend two minutes memorizing a random list of words, then get a blank piece of paper and try to write down as many of the words that you can remember.