Dumb dumb needs dice help

I don't know if this is meant to go in RP tutoring or whatever, but it is a simple question.
I still can't get my head around this dice thing, I am usually a quick learner and tried to figure it out myself.
But I need a little pin point on something.

So i've rolled a knife
ElX8X5Kjknife


ok so I put the '2132' into the damage calculator.
I've done it as a knife in stomach and the number I get back is 2138.5
I see people get like a single digit number? what am I doing wrong D:

knife