Young children spend a much greater amount of time on practicing multiplication facts compared to understanding the concept of multiplication. When students have long-term, foundational concepts rather than a series of fragmented algorithms or facts, they are more likely to understand and generalize the mathematics. Using generalized models that represent both concepts and procedures is an important part of students' development of mathematical understanding. This article claims that the concept of unit and intermediate unit has the potential to establish a general model of multiplication, and that the heart of multiplication is the change of units. When students have sufficient knowledge of the general concept of multiplication, they can have a better sense of multiplication of all real numbers.