diff --git a/src/geometry/circle.py b/src/geometry/circle.py
index f8ae2ea..0a23b4a 100644
--- a/src/geometry/circle.py
+++ b/src/geometry/circle.py
@@ -35,3 +35,19 @@ def calculate_circ(r):
     """
     circ = 2 * pi * r
     return circ
+
+
+def calculate_diam(r):
+    """
+    Calculate the diameter of a circle.
+
+    Parameters
+    ----------
+    r : float, the radius
+
+    Returns
+    -------
+    float : the diameter of the circle
+    """
+    diam = 2 * r
+    return diam