The average size of a human heart is roughly similar to that of a closed fist. It’s approximately 12 centimeters (about 4.7 inches) in length, 8-9 centimeters (around 3.1-3.5 inches) in width, and about 6 centimeters (approximately 2.4 inches) in thickness. Of course, there can be variations in heart size based on an individual’s age, sex, and overall health.