The current High-Security Government requirement for document destruction, NSA/CSS Spec 02-01 states that a Level 6 Paper Shredder (NSA Approved) must produce a maximum particle in which,

"90% of shredded particles shall not exceed 5 square millimeters and the remaining 10% of particles shall not exceed 10 square millimeters."  

The old standard, Level 5 security, allowed for a larger particle size.  Watch the video below for a detailed explanation.

NSA APPROVED LEVEL 6 PAPER SHREDDERS [Click below]

Personal	Small Office	Large Office	Industrial

The US Government produces an Evaluated Products List (EPL 02-01) that contains a listing of all shredders that have been evaluated by the National Security Agency (NSA) or its designee and meet the performance requirements of NSA/CSS Specification 02-01, High Security Paper Shredders.  Inclusion of a product in the EPL is not an endorsement by NSA or the U.S. Government.  Find a link to the EPL at the bottom of this post.

Attached below is the EPL (Evaluated Products List)