Here's how to convert 5 and a half centimeters to millimeters:

* Know the conversion: 1 centimeter (cm) is equal to 10 millimeters (mm).

* Convert the whole number: 5 cm * 10 mm/cm = 50 mm

* Convert the half centimeter: 0.5 cm * 10 mm/cm = 5 mm

* Add the results: 50 mm + 5 mm = 55 mm

Therefore, 5 and a half centimeters is equal to 55 millimeters.