To evenly size two or more objects, first select them (see Selecting multiple objects) and then use any of the following buttons:
Make Same Width. All the selected objects are adjusted to have the same width.
Make Same Height. All the selected objects are adjusted to have the same height.
Make Same Size. All the selected objects are adjusted to have the same height and width.
All these commands are also available under Same Size in the Format menu.
See also: