Genetics is one of the biggest factors determining a cat's size. Different breeds of cats have different genetic traits that can affect their size, weight, and overall physical appearance. Gender can also play a role in determining the size of a cat. Typically, male cats tend to be larger and heavier than females. The food and nutrition a cat receives can also impact their growth and size. Health, exercise, neutering/spaying, age, and the number of siblings a cat has can also impact its growth and size.