You can set the column widths in the properties window in the VBE editor in
design mode.

From the VBA help file:

Unless specified otherwise, column widths are measured in points. To specify
another unit of measure, include the units as part of the values. The
following examples specify column widths in several units of measure and
describe how the various settings would fit in a three-column list box that
is 4 inches wide.

Setting
90;72;90
Effect
The first column is 90 points (1.25 inch); the second column is 72 points (1
inch); the third column is 90 points.