To Get unit conversion value of item in Ax 2012 you can use below code. UnitOfMeasureConverter_Product is a class which has different method to give you converted value.
Here example is showing to get conversion value from liter to kilo gram.
Here example is showing to get conversion value from liter to kilo gram.
UnitOfMeasureConverter_Product unitConverter = UnitOfMeasureConverter_Product::construct();
unitConverter.parmProduct(InventTable::find("TestIte",true).Product);
unitConverter.parmFromUnitOfMeasure(UnitOfMeasure::unitOfMeasureIdBySymbol("ltr"));
unitConverter.parmToUnitOfMeasure(UnitOfMeasure::unitOfMeasureIdBySymbol("kg"));
unitConverter.parmRoundAbsoluteValue(NoYes::Yes);
unitConverter.parmApplyRounding(NoYes::Yes);
info(strFmt("%1",unitConverter.convertValue(1)));