The answer depends on which country's penny the question is about. Many countries use a penny as a minor currency unit and since you have not bothered to share the name of the country, I cannot provide a more useful answer.
19 millimeters
English penny of today: 3,56 g and 20,32 mm.
You would use millimetres.
The answer depends on which country's penny the question is about. Many countries use a penny as a minor currency unit and since you have not bothered to share the name of the country, I cannot provide a more useful answer.
It is .25 mm that is the larger diameter
The circumference of a circle with a 10 millimeter diameter is about 31.42 mm
millimeter
The diameter of a US penny is 0.01905 metres
The diameter is twice the radius so the answer is 12 millimeters.
The diameter of the bullets
Diameter of an Australian penny (no longer currency) is 1 and 3/16".
The answer is 5.21 millimeter's.