I found the solution on how to convert the Classificaiton unit values to a different measuring system as per selected preference at Org Level.
attrValue is AbsrtractValue from a IBA holder like WTPart.
classAttr is the Classification Attribute.
orgPreference is the Measuring System selected at org Prefence.
Solution:
value=IBAValueUtility.getLocalizedIBAValueDisplayString(attrValue, locale);
String preferenceUOM = classAttr.getDisplayUnits(orgPreference);
value=value.replaceAll(classAttr.getQoM().getBaseUnit(), "");
value= value.trim();
Unit u= new Unit(value, classAttr.getQoM().getBaseUnit());
DecimalFormat df = new DecimalFormat("####.####");
double dd=u.convert(preferenceUOM);
value=df.format(dd);
value = value.concat(" "+preferenceUOM);