2.1.1335 Part 4 Section 18.104.22.168, gridCol (Table Grid Column)
a. The standard specifies that the w attribute defines the width of the column in EMUs.
In Office, the width of the column is equal to or greater than the sum of the marL and marR attributes of the tcPr element plus two points for each cell in the column. One point is equal to 12700 EMUs.