What is the relationship between diameter and radius?

The radius is exactly half the diameter. Diameter is the distance across a circle through its center; radius is the distance from the center to the edge.

How do I find circumference from diameter?

Multiply the diameter by π (approximately 3.14159). For example, a circle with diameter 10 cm has circumference = 10 × π ≈ 31.42 cm.

Diameter to Radius Converter Calculator

Convert diameter to radius or radius to diameter instantly. Also calculates circumference and area for any circle. Supports mm, cm, m, km, inches, feet, yards, and miles.

Complete User Guide

Choose direction (Diameter → Radius or Radius → Diameter), enter the value, select a unit, and click Convert. The result also shows circumference and circle area.

The Mathematical Formula

Radius = Diameter ÷ 2; Circumference = π × Diameter; Area = π × Radius²

r = d/2. Circumference = π × d. Area = π × r². Pi (π) ≈ 3.14159265.

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