How is gelatine sold in U.S. grocery stores? I'm interested in trying a recipe from Alton Brown for marshmallow. I'm not sure what exactly "3 packages unflavored gelatin" refers to.

How much gelatine (in weight) is included in a standard package of gelatine in the U.S.? And what bloom* would that be?

Probably has no bearing, but is that likely to be powdered or leaf gelatine?

* Actually not sure what bloom is used for gelatine from Swedish stores. Awaiting a reply from Dr. Oetker's customer service on that point :-)
The packs typically contain the equivalent of 15mL of gelatine and are in powder form.  Each pack is measured to set 500mL or two cups of liquid.  As far as weight, it feels like about 6-7 grams of gelatin.

The dominant brand seems to be knox.  



As for the bloom, I'm not really sure as I haven't seen it published on the label.  However, I have actually made marshmallow using the same Alton Brown recipe and it seemed pretty tolerant.  So slightly different bloom should be fine.  I also deviated with the corn syrup and didn't use it (I avoid corn).  The end result was still awesome.