You can't convert a diameter directly to centimeters because a diameter is a measurement of distance across a circle, not a unit of length.

To convert a diameter to centimeters, you need to know:

1. The diameter's unit of measurement: Is it inches, millimeters, feet, etc.?

2. The conversion factor between that unit and centimeters.

For example:

* If you have a diameter of 5 inches, you would need to multiply 5 by 2.54 (since there are 2.54 centimeters in an inch) to get 12.7 centimeters.

In short, you can't say how many centimeters are in 1 diameter without knowing what the diameter is measured in.