diff --git a/beer/extras.py b/beer/extras.py
index 9069ffe..1d120c0 100644
--- a/beer/extras.py
+++ b/beer/extras.py
@@ -86,3 +86,12 @@ def get_batches(api_user, api_key, batch=''):
         data = data + get_batches(batch=last_id)
 
     return data
+
+def sg_plato(sg):
+    """Convert specific gravtiy to °P."""
+    sg = float(sg)
+    return (-1*616.868) + (1111.14*sg) - (630.272*sg**2) + (135.997*sg**3)
+
+def plato_sg(plato):
+    """Convert °P to specific gravtiy."""
+    return 1 + (plato / (258.6 - (plato/258.2) * 227.1))