diff --git a/src/geometry/sphere.py b/src/geometry/sphere.py
index 47a5e7c..fdf2e85 100644
--- a/src/geometry/sphere.py
+++ b/src/geometry/sphere.py
@@ -1,13 +1,13 @@
 from math import pi
 
 
-def calculate_surface_area(r):
+def calculate_volume(r):
     """ 
-    Calculate the surface area of a sphere. 
+    Calculate the volume of a sphere. 
 
     This uses the standard mathematical calculation: 
 
-    $4\pi r ^2$
+    $(4 * \pi r ^3) / 3$
 
     Parameters
     ----------
@@ -15,6 +15,21 @@ def calculate_surface_area(r):
 
     Returns
     -------
+    float : the volume of the sphere
+    """
+
+    volume = (4 * pi * r **3) / 3
+    return volume
+
+
+def calculate_surface_area(r):
+    """ 
+    Calculate the surface area of a sphere. 
+
+    This uses the standard mathematical calculation: 
+
+    $4\pi r ^2$
+
     float : the surface area of the sphere
     """
     surface_area = 4 * pi * r **2