Dus met andere woorden de hoeveelheid elementen dat het kortetermijngeheugen kan onthouden staat vast.

In an early and highly influential article, The Magical Number Seven, Plus or Minus Two the psychologist George Millersuggested that human short-term memory has a forward memory span of approximately seven items plus or minus two. More recent research has shown that this "magical number seven" is roughly accurate for college students recalling lists of digits, but memory span varies widely with populations tested and with material used. For example, the ability to recall words in order depends on a number of characteristics of these words: fewer words can be recalled when the words have longer spoken duration; this is known as the word-length effect, or when their speech sounds are similar to each other; this is called the phonological similarity effect. More words can be recalled when the words are highly familiar or occur frequently in the language.

Recall performance is also better when all of the words in a list are taken from a single semantic category (such as sports) than when the words are taken from different categories. According to the available evidence, the best overall estimate of short-term memory is about four pieces or "chunks" of information.

Chunking is the process with which we can expand our ability to remember things in the short term. Chunking is also a process by which a person organizes material into meaningful groups. Although the average person may only retain about four different units in short-term memory, chunking can greatly increase a person's recall capacity. For example, in recalling a phone number, the person could chunk the digits into three groups: first, the area code (such as 215), then a three-digit chunk (123) and lastly a four-digit chunk (4567). This method of remembering phone numbers is far more effective than attempting to remember a string of 10 digits.

Practice and the usage of existing information in long-term memory can lead to additional improvements in one's ability to use chunking. In one testing session, an American cross-country runner was able to recall a string of 79 digits after hearing them only once by chunking them into different running times (e.g. the first four numbers were 1518, a three-mile time.)

It is very difficult to demonstrate the exact capacity of STM due to the fact that it will vary depending on the nature of the material to be recalled. Until now, there is no way of defining the basic unit of information to be stored in the STM store. It is also possible that STM is not the store described by Atkinson and Shiffrin. In that case, the task of defining the task of STM becomes even more difficult.

Some other factors are listed below: Reading Aloud: Digital spans tend to increase if the digits are read aloud by participants instead of being read sub-vocally. Baddley (1999) suggests that the sounds are also stored in the echoic store which makes storing it easier.