diff --git a/pygal/config.py b/pygal/config.py
index 17e127c..8521cda 100644
--- a/pygal/config.py
+++ b/pygal/config.py
@@ -154,6 +154,10 @@ class Config(object):
         False, bool, "Value", "Display values in human readable format",
         "(ie: 12.4M)")
 
+    value_formatter = Key(
+        None, type(lambda: 1), "Value",
+        "A function to convert numeric value to strings")
+
     logarithmic = Key(
         False, bool, "Value", "Display values in logarithmic scale")
 
diff --git a/pygal/graph/base.py b/pygal/graph/base.py
index 547e96f..0835ef6 100644
--- a/pygal/graph/base.py
+++ b/pygal/graph/base.py
@@ -80,7 +80,8 @@ class BaseGraph(object):
     @property
     def _format(self):
         """Return the value formatter for this graph"""
-        return humanize if self.human_readable else str
+        return self.value_formatter or (
+            humanize if self.human_readable else str)
 
     def _compute(self):
         """Initial computations to draw the graph"""