To determine the correct size mirror for a 36-inch vanity, there are different approaches. Here are some guidelines from the search results:

• As a rule of thumb, the mirror above a 36-inch vanity should be about 30-34 inches wide, and the height of the mirror depends on the height of the ceiling.
• Another rule of thumb suggests that the right mirror size for a 36-inch vanity is 32 inches wide and 24 inches high.
• To calculate the correct size rectangular mirror for a bathroom, follow these steps:
  • Measure the height of the ceiling.
  • Get the height and width of the vanity.
  • Subtract 4 inches from the width of the vanity. This is the width of the mirror.
  • Add 12 inches to the height of the vanity. Subtract the answer from the height of the ceiling. This is the height of the mirror.
• When choosing a mirror for a 36-inch vanity, make sure it is at least 36 inches wide to perfectly frame the vanity.
• Some people may opt to use two mirrors instead of one for a double vanity, but the standard size for each mirror is still four inches smaller than the width of the vanity.
• In a discussion on Houzz, a user suggests leaving at least 3 inches between the sconce shade and mirror and the sconce and the wall, so 3" + 3" + width of sconce. They have a 24" mirror over a 36" vanity.

Based on these guidelines, the size of the mirror for a 36-inch vanity could be 30-34 inches wide and 24-48 inches high, depending on the height of the ceiling and personal preference.