RowMinHeight

RowMinHeight is an option for GridBox which specifies the minimum total height in units of font size that should be allowed for each row.

The default setting RowMinHeight->1 forces each row to have a total height which at least accommodates all the characters in the current font.

RowMinHeight->0 reduces the total height of each entry as much as possible, allowing entries containing characters such as x and X to be different heights.

See The Mathematica Book: Section 2.8.11.

See also: RowSpacings, RowAlignments, RowsEqual, ButtonMinHeight.