Understanding Bathroom Mirror Sizing
This calculator applies two common interior-design rules of thumb to your vanity measurements: a width rule and a height rule. Together they turn a vanity width, a countertop height, and a user's height into a recommended mirror width and height, plus the exact heights from the floor for the mirror's bottom and top edges.
The formulas
- Mirror width = Vanity width − (2 × side margin). Leaving a margin of about 2 to 3 inches on each side of the vanity keeps the mirror from crowding the wall or overlapping outlets and sconces. For a double-sink vanity, the same formula is applied to half the vanity width for each of the two mirrors.
- Bottom edge height (from the floor) = Countertop height + bottom clearance. A gap of roughly 4 to 6 inches above the counter or backsplash is standard.
- Top edge height (from the floor) = (Tallest user's height − 4 in) + 3 in buffer. The "height minus 4 inches" term approximates eye level below the top of the head; the buffer keeps the crown of the head in frame too.
- Mirror height = Top edge height − Bottom edge height.
Reading the results
The width tells you how wide a mirror to shop for; the height tells you how tall. The bottom and top edge heights tell an installer exactly where to mark the wall — measured straight up from the finished floor, not from the counter. Always double-check the recommended top edge against the actual wall space: a window, medicine cabinet, or light fixture above the vanity can force a shorter mirror than the formula suggests.
Frequently Asked Questions
How wide should a bathroom mirror be?
A common rule of thumb is to leave about 2 to 3 inches of wall showing on each side of the vanity, so Mirror Width = Vanity Width − 2 × side margin. For a 36 inch vanity with a 2.5 inch margin per side, that works out to 31 inches.
How high should a bathroom mirror be mounted?
Leave roughly 4 to 6 inches of clearance between the countertop or backsplash and the bottom edge. The top edge should clear the tallest household member's eye level — approximated as their height minus about 4 inches — plus a small buffer.
What if my vanity has two sinks?
Choose "Double sink" and the calculator sizes each of two mirrors using half the vanity width, so each mirror can be centered over its own sink. Alternatively, treat the vanity as a single width and hang one large mirror.
Does this account for ceiling height or light fixtures?
No — the calculator only uses vanity width, countertop height, and user height. Always measure the actual wall space, including any window, medicine cabinet, sconce, or light fixture, before buying a mirror sized by this tool.