How big is your vanity? Some people like to have the mirror the exact same length as the vanity, or smaller. If you are unable to find one that is the exact same length, opt for a smaller one – this will be easier to centre and style around.
Think about the shape you want for your mirror!
Oval bathroom mirrors elongate the vanity area. These are perfect for smaller vanities with a single bowl, or double bowl vanities where two mirrors will be needed. Because of the oval shape, the space will look higher. Similarly, a round bathroom mirror can create the same effect, but width wise.
An arched bathroom mirror is best styled with larger vanities with a single bowl. The arched shape brings the vanity and the mirror together.
Rectangle and square edged bathroom mirrors are great for making the most out of your space. This style of mirror is perfect for longer vanities with a double bowl as this creates a unison between the individual bowls.