In the case of a regular polygon, the diameter is the diameter of the circumscribed circle of the polygon. If the polygon has an even number of sides, the diameter joins two opposite vertices and passes through the centre of the polygon.
The term also refers to the measure of this chord.
- The radius of a circle is half the length of the diameter.
- The diameter of a square is the length of its diagonal :
The word “diameter”, derived from the Greek δια-μετρητοσ, means “measure”.