Get The size of the Text in unity UI

Hello i am using unity 5.4
I have a image having a child Text. i want to scale the image based on the string size given to the text. i am using following code to get the work done.

 m_textBgImage = Instantiate (m_textBgPrefabs);    // This is a image prefab has text as its child 
 m_chatText = m_textBgImage.GetComponentInChildren<Text> ();
 
 m_chatText.text = m_textToDisplay;
 Vector2 widthHeight = GetSizeOfWord (m_textToDisplay);
 textBgImage.GetComponent<RectTransform>().sizeDelta = widthHeight;
 
 
 
 Vector2 GetSizeOfWord(string word)
     {
         float width = 0.0f;
         float biggestWidth = 1.0f;
         float biggestHeight = 0.0f;
         int spaceCounts = 0;
 
 
         print ("m_chatText.fontSize : "+m_chatText.fontSize); 
         foreach (char c in word)
         {
             CharacterInfo charInfo;
             if (c == ' ') 
             {
                 spaceCounts++;
             }
             else 
             {
                 m_chatText.font.GetCharacterInfo (c, out charInfo, m_chatText.fontSize);
                 width += charInfo.glyphWidth;
 
                 if (biggestWidth < charInfo.glyphWidth) {
                     biggestWidth = charInfo.glyphWidth;
                 }
                 if (biggestHeight < charInfo.glyphHeight) {
                     biggestHeight = charInfo.glyphHeight;
                 }
                 print ("Char : "+c);
                 print ("Advance : "+charInfo.advance);
                 print ("Height : "+charInfo.glyphHeight);
                 print ("Width : "+charInfo.glyphWidth);
                 print ("Index : "+charInfo.index);
                 print ("Bearing : "+charInfo.bearing);
                 print ("MaxX : "+charInfo.maxX);
                 print ("MaxY : "+charInfo.maxY);
                 print ("Size : "+charInfo.size);
                 print ("Style : "+charInfo.style);
                 print ("uvBottomLeft : "+charInfo.uvBottomLeft);
                 print ("uvBottomRight : "+charInfo.uvBottomRight);
                 print ("uvTopLeft : "+charInfo.uvTopLeft);
                 print ("uvTopRight : "+charInfo.uvTopRight);
             }
         }
         print ("Space count : "+spaceCounts);
         float textWidth = width + (biggestWidth * spaceCounts);
         float textHeight = Mathf.Floor (textWidth / m_maxLengthOfText);
         textWidth = Mathf.Min( m_maxLengthOfText,width);
         print ("W : " + textWidth + " H : " + textHeight * biggestHeight);
         return new Vector2(textWidth, textHeight * biggestHeight);
     }

The "out charInfo" is most of the time outputting zero value and all the print statements displays zero, and randomly once in a blue moon it gets the correct value, the height and width of the character.
Does anyone know why i am getting zero values , where i am missing out?