Hello,
I do not know if Michael's correct answer will solve your issue totally? Perhaps I do misunderstand, but think you want not only to know how to resize objects more precisely (which can be done by the Transform accordion, although I prefer using shorcut keys for small resizing/moving, see: Shortcut keys for Moving/Resizing ) but also how to have the same size for all buttons. And using the Apply to all from the Transform accordion is not useful because, which I regret tremendously, this accordion will not only apply the size settings to all objects of same type (or style) but also the X-Y coordinates of its registration point (mostly top left of the bounding box) and if you use 5.5 also the rotation if the source object has a rotation. I have already asked multiple times to have the size separated from those other properties, but apparently no one else has issues with that, so request is not top priority.
Another possibility would exist if size was part of the object style, but it is not either.
I could offer some suggestions, all workarounds, but first could you tell me which version you are using and, if you are talking about Text buttons or are you willing to create your own image buttons or to replace the buttons by an image with a transparent button on top of it (you'll lose the states in that case).
Anyway, for text buttons: be sure to uncheck the AutoSize Buttons in Preferences, Defaults.
To resize buttons on the same slide to the same size, you can use the right click menu on the selection, Align, Resize to Same Size
Lilybiri
