How this calculator works
A bathroom mirror is sized from the vanity it sits over. The common rule is that the mirror spans the vanity from edge to edge, so the recommended width is the vanity width, or half of it for two mirrors that meet in the middle. The height follows from the two heights you can measure: the bottom edge sits a short gap above the vanity top so the backsplash and taps stay clear, and the top edge lines up with a comfortable height such as the top of the door frame. The difference between those two heights is the mirror height. Keeping the top below the ceiling leaves room for a light fixture and stops the mirror looking cramped.
Formula
bottom = vanity height + gap above the vanity. mirror height = height of the top edge - bottom. rectangular width = vanity width, or vanity width / 2 for two mirrors. round diameter = the smaller of the recommended width and height. space above = ceiling height - top edge height.
Worked example
A vanity 85 cm tall and 90 cm wide under a 2.4 m ceiling, with a 15 cm gap and a top edge at 2.0 m, gives a bottom edge at 100 cm, a mirror 100 cm tall and 90 cm wide, and 40 cm of ceiling left above it. Two mirrors over the same vanity would be about 45 cm wide each.
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Frequently asked questions
How high should a bathroom mirror hang?
A common guideline is to keep the bottom of the mirror about 15 cm above the vanity top and the top of the mirror at eye level or at the height of the door frame, roughly 2 m from the floor. The exact figure depends on how tall the people using it are.
Can the mirror be wider than the vanity?
It can, and a wider mirror can make a small bathroom feel larger. A mirror narrower than the vanity tends to look undersized; if the wall is narrow, use a mirror that at least spans the basin.
Do I need space above the mirror?
If you plan a light bar or sconces above the mirror, leave room for the fixture. A mirror that reaches the ceiling leaves only side lighting as an option.
What about an arched or oval mirror?
Use the round or oval option and check the diameter. An oval mirror fits the same height and width envelope as a round one, with the diameter standing in for both dimensions.