diff --git a/rowers/dataprep.py b/rowers/dataprep.py
index 5ce1a5d6..57f34316 100644
--- a/rowers/dataprep.py
+++ b/rowers/dataprep.py
@@ -210,6 +210,12 @@ def clean_df_stats(datadf,workstrokesonly=True,ignorehr=True,
         datadf.loc[mask,'pace'] = np.nan
     except KeyError:
         pass
+
+    try:
+        mask = datadf['efficiency'] < 0.
+        datadf.loc[mask,'efficiency'] = np.nan
+    except KeyError:
+        pass
         
     try:
         mask = datadf['pace']/1000. < 60.
@@ -1423,6 +1429,14 @@ def dataprep(rowdatadf,id=0,bands=True,barchart=True,otwpower=True,
             totalangle = savgol_filter(totalangle,windowsize,3)
             effectiveangle = savgol_filter(effectiveangle,windowsize,3)
 
+        velo = 500./p
+
+        ergpw = 2.8*velo**3
+        efficiency = 100.*ergpw/power
+
+        efficiency = efficiency.replace([-np.inf,np.inf],np.nan)
+        efficiency.fillna(method='ffill')
+            
         data['wash'] = wash
         data['catch'] = catch
         data['slip'] = slip
@@ -1432,6 +1446,7 @@ def dataprep(rowdatadf,id=0,bands=True,barchart=True,otwpower=True,
         data['drivelength'] = drivelength
         data['totalangle'] = totalangle
         data['effectiveangle'] = effectiveangle
+        data['efficiency'] = efficiency
         
     if otwpower:
 	try:
diff --git a/rowers/metrics.py b/rowers/metrics.py
index 4fb00b02..c65cbcc0 100644
--- a/rowers/metrics.py
+++ b/rowers/metrics.py
@@ -22,6 +22,7 @@ axes = (
     ('totalangle', 'Drive Length (deg)',40,140,'pro'),
     ('effectiveangle', 'Effective Drive Length (deg)',40,140,'pro'),
     ('rhythm', 'Stroke Rhythm (%)',20,55,'pro'),
+    ('efficiency', 'OTW efficiency (%)',0,110,'pro'),
      ('None', 'None',0,1,'basic'),
     )
     
diff --git a/rowers/models.py b/rowers/models.py
index 9bb87132..e880ca24 100644
--- a/rowers/models.py
+++ b/rowers/models.py
@@ -536,6 +536,7 @@ class StrokeData(models.Model):
     rhythm = models.FloatField(default=1.0,null=True,verbose_name='Rhythm')
     totalangle = models.FloatField(default=0.0,null=True,verbose_name='Total Stroke Length (deg)')
     effectiveangle = models.FloatField(default=0.0,null=True,verbose_name='Effective Stroke Length (deg)')
+    efficiency = models.FloatField(default=-1,null=True,verbose_name='OTW Efficiency')
     
 # A wrapper around the png files
 class GraphImage(models.Model):
diff --git a/rowers/views.py b/rowers/views.py
index fc671f05..cab19bb5 100644
--- a/rowers/views.py
+++ b/rowers/views.py
@@ -5618,7 +5618,7 @@ def workout_flexchart3_view(request,*args,**kwargs):
         axchoicespro.pop('totalangle')
         axchoicespro.pop('effectiveangle')
         axchoicespro.pop('peakforceangle')
-        
+        axchoicespro.pop('efficiency')
         
         return render(request,
 		      'flexchart3otw.html',