Magic number 7+-2

Number of items that can be held in short term memory: 7 +/- 2

Cause

Memory span refers to the longest list of items (e.g., digits, letters, words) that a person can repeat back in correct order on 50% of trials immediately after presentation. A study by cognitive psychologist George A. Miller observed that memory span of young adults is approximately seven items. Later research on short-term memory and working memory revealed that memory span is not a constant.