The diameter is a straight line that passes through the center of a circle or sphere, connecting two points on its boundary. It is the longest distance across the circle and is twice the length of the radius, which is the distance from the center to the edge. The formula to calculate the diameter is simple: Diameter = 2 × Radius. In geometry, the diameter is an important measurement used in various calculations, including finding the area and circumference of a circle. The circumference can be calculated using the formula Circumference = π × Diameter, where π (pi) is approximately 3.14. Understanding the diameter helps in many practical applications, such as engineering and design.