How is morphine measured when given through an IV?

Ever since I had my gallbladder out I have been having episodes of intense pain, sometimes to the point that I have to go to the hospital. I had never had morphine before until I started going to the hospital during all this. During the past five months I had to have five morphine injections through an IV. I don't particularly like having to be given morphine all the time but it's the only thing that sort of, key words, SORT OF works to calm the pain. So my question is how is morphine measured (mg, ml, cc, etc) when given through an IV? And was in a normal dose? The last time I was in the hospital they gave me "400" of morphine and then about fifteen mins later another "400" of it. That seems like an awful lot to me and I could feel it tingle through my body but maybe that's actually normal? I'm just curious.