Diameter 17.8 cm.

A seven-inch pizza refers to a pizza with a diameter of 17.8 cm. The inch of pizza refers to inches, 1 inch is 2.54 cm, and 7 inches is 17.8 cm.

The inch is a unit of length used in the United Kingdom, the English abbreviation is in, and the symbol for inches is. 1 inch equals 2.54 centimeters, 12 inches equals 1 foot, and 36 inches equals 1 yard.