diff --git a/Code/Mantid/MantidQt/CustomInterfaces/inc/MantidQtCustomInterfaces/ConvFit.h b/Code/Mantid/MantidQt/CustomInterfaces/inc/MantidQtCustomInterfaces/ConvFit.h
index 105c01735989e775177ad8dcd39d08140f84cd96..d349967ab549f4ceb895d62d1e0a54cc69df5d95 100644
--- a/Code/Mantid/MantidQt/CustomInterfaces/inc/MantidQtCustomInterfaces/ConvFit.h
+++ b/Code/Mantid/MantidQt/CustomInterfaces/inc/MantidQtCustomInterfaces/ConvFit.h
@@ -47,6 +47,7 @@ namespace IDA
 
   private:
     boost::shared_ptr<Mantid::API::CompositeFunction> createFunction(bool tieCentres=false);
+    double getInstrumentResolution(std::string workspaceName);
     QtProperty* createLorentzian(const QString &);
     void createTemperatureCorrection(Mantid::API::CompositeFunction_sptr product);
     void populateFunction(Mantid::API::IFunction_sptr func, Mantid::API::IFunction_sptr comp, QtProperty* group, const std::string & pref, bool tie);
diff --git a/Code/Mantid/MantidQt/CustomInterfaces/src/ConvFit.cpp b/Code/Mantid/MantidQt/CustomInterfaces/src/ConvFit.cpp
index 169601acfb8d8102fc4e88310ffd07b829ca406b..574a21684cba2a653a0bf79e1851a3d7a7c655d7 100644
--- a/Code/Mantid/MantidQt/CustomInterfaces/src/ConvFit.cpp
+++ b/Code/Mantid/MantidQt/CustomInterfaces/src/ConvFit.cpp
@@ -472,6 +472,26 @@ namespace IDA
     product->applyTies();
   }
 
+  double ConvFit::getInstrumentResolution(std::string workspaceName)
+  {
+    using namespace Mantid::API;
+
+    double resolution = 0.0;
+    try
+    {
+      MatrixWorkspace_sptr ws = AnalysisDataService::Instance().retrieveWS<MatrixWorkspace>(workspaceName);
+      Mantid::Geometry::Instrument_const_sptr inst = ws->getInstrument();
+      std::string analyser = inst->getStringParameter("analyser")[0];
+      resolution = inst->getComponentByName(analyser)->getNumberParameter("resolution")[0];
+    }
+    catch(Mantid::Kernel::Exception::NotFoundError &e)
+    {
+      resolution = 0;
+    }
+      
+    return resolution;
+  }
+
   QtProperty* ConvFit::createLorentzian(const QString & name)
   {
     QtProperty* lorentzGroup = m_cfGrpMng->addProperty(name);
@@ -653,6 +673,14 @@ namespace IDA
     {
       showInformationBox(exc.what());
     }
+
+    // Default FWHM to resolution of instrument
+    double resolution = getInstrumentResolution(m_cfInputWSName.toStdString());
+    if(resolution > 0)
+    {
+      m_cfDblMng->setValue(m_cfProp["Lorentzian 1.FWHM"], resolution);
+      m_cfDblMng->setValue(m_cfProp["Lorentzian 2.FWHM"], resolution);
+    }
   }
 
   void ConvFit::plotGuess(QtProperty*)