When choosing the size of your mirror, you should consider not just function, but also proportion. To create a balanced look, think about the size of your mirror relative to that of your vanity. Typically, vanity mirrors are not wider than the vanity itself, with some exceptions we will discuss a little later.
Before you do anything, think about what your ideal bathroom would be. Forget constraints of money and space; just imagine what you want and what the intended purpose will be. Who is this bathroom for? Is it a master bathroom? A powder bathroom? A kid’s bathroom? How often will it get used and what will the function be?
Pay attention to the age of your home and the remodels done by previous homeowners. Putting new tile over a foundation rife with dry rot or severely outdated or junky plumbing is only delaying a potentially huge problem down the road. You may want to wait until you can do a complete job right.
In fact, centering a mirror on the sink and then adding a second mirror symmetrical to the first can make the whole composition look more pleasingly balanced, compared with using just a single mirror. Another reason to use smaller mirrors is, of course, to allow some room for sconces to sit in between. Vanity light can be located in various places, but placing it to the sides of the mirror lights the face well, so it is both beautiful and functional.