80 centimeters. Ruler is a unit of length, and the conversion is advertised as 1 foot = 10 inch, so 2 feet equals 2 times 10 equals 20 inches, and 2 feet 4 inches equals 20+4 equals 24 inches. Inch is a traditional unit of length in China, which is converted into 1 inch =3.33 cm, and cm is the unit of length measurement, so 24 inches is equal to 24 times 3.33, which is about 80 cm, that is, the waist circumference of 2 feet 4 inches is 80 cm.