Contrary to popular belief, Peeps may vary as much as ± 14 millimeters due to barometric pressure and inaccuracies in the extrusion molding process.
 

Each peep's weight is verified and then cross checked between an unemployed circus weight guesser and a postal scale on loan from the Motel 6 managers office.

NASA uses a sophisticated water displacement test to determine marshmallow to air ratio.  An unusually high air content in a peep can result in unpredictable growth upon entering an alien atmospheres or gravitational field.  A peep that was sent on a Jupiter fly-by mission expanded to the size of a two story house instantly destroying the command capsule (constructed from a Chock-Full "O" Nuts coffee can and packing peanuts) and entering low orbit over the planet.