Where is size, make equal in Visio 2013

Use the Size and Position window (menu View -> Task Panes). Select the shapes you want, then to change the width of them all just types in a new width.

You can use the F4 key to duplicate the last keystroke for instance, if you choose a shape, put in the height that you want, then choose the next shape and hit the F4 key, it will duplicate the same height, then you won't have to physically type the change for each item - hope that helps