How to Measure for a Mirror That Actually Fits

A mirror fails on the tape measure, not on the wall. By the time a custom mirror is cut, polished, and carried into your bathroom, the size is fixed — glass does not stretch, and it does not forgive a quarter inch the way a wood trim piece does. Most of the bad fits I get called to fix started the same way: somebody measured once, in the middle, rounded to a nice number, and ordered. The wall was not square, the vanity was not centered, or a faucet or outlet was sitting exactly where the glass needed to go. Measuring a mirror well takes ten extra minutes. Here is the order we do it in, and the checks that matter.

Measure the finished wall, not the plan

Take your numbers after tile, backsplash, and paint are done, with the vanity and faucets installed if at all possible. A plan dimension is what the room was supposed to be. Tile thickness, a backsplash that runs a little high, or a vanity shifted half an inch to clear plumbing all change the space the mirror actually has to live in. Use a metal tape, not a cloth one, and write down the exact reading — to the nearest sixteenth — before you decide what size to order. Fabricators cut to your finished size, so your job at this stage is not to make the number pretty. It is to record the truth, in three places, for both width and height.

Width: start from the vanity, then check the wall

For a typical bathroom mirror, width is a design decision with practical limits. A reliable approach is to keep the mirror a few inches narrower than the vanity — two to four inches in from each side — so it reads as intentional and leaves room for sconces and tile edges. A wall-to-wall mirror is a different tolerance problem: it has to fit between two walls that are rarely parallel, so it needs the out-of-square check below and usually a template. For a double vanity, decide early whether you want one large mirror or two separate mirrors centered over each sink. One large piece looks clean; two pieces are easier to handle and replace, and center on each faucet. Mark each sink centerline with painter's tape and measure to that line, not to your eye.

Height: bottom, top, and the people using it

Height has three anchors. At the bottom, leave a small, consistent gap above the backsplash — enough that water and cleaning spray are not trapped against the mirror edge. Sitting a large mirror directly on the backsplash is asking for edge damage and moisture creep behind the silvering. In the middle, the mirror has to serve the people who use the room: its center should sit roughly at eye level, checked standing at the sink, not back by the door. At the top, respect the light fixture. Measure to the bottom of the fixture and the ceiling, and decide whether the mirror stops below the light, runs behind it, or is notched around it. A mirror that was supposed to clear a fixture by an inch and clears it by nothing is the most common height mistake we see.

The clearances people forget

• Faucets and handles. Measure how tall the faucet rises and how far the handles swing. A tall vessel faucet or a lever that leans back can hit a mirror that sits low or leans on clips.
• Outlets and switches. Note every outlet, switch, and towel bar on the mirror wall with its distance from the left edge and from the counter. If an outlet falls inside the mirror area, it needs a cutout in exactly the right place — or the mirror size needs to change. Cutouts cannot be added after the mirror is made.
• Doors and side walls. Check what swings nearby: a bathroom door, a medicine cabinet door, a shower door. A mirror that fits the wall but gets clipped by a swinging door was measured in isolation.
• Mounting and weight. Large mirrors are heavy. Note whether the wall is drywall, tile, or plaster, and where the studs are if you can find them. That decides clips, channel, or adhesive — see our custom mirror services for how we mount large pieces safely.

The out-of-square check — do not skip it

Measure width at the top, in the middle, and at the bottom. Measure height on the left, in the center, and on the right. If all six numbers match, you have an unusually honest wall. More often they differ by an eighth to a quarter inch, and on older Los Angeles homes, sometimes more. That difference decides the order size: a rectangular mirror has to fit the smallest dimension, with the gaps taken up evenly, or it has to be cut to a template that follows the wall. For a tight wall-to-wall or floor-to-ceiling fit, we make a full-size paper or cardboard template, tape it where the mirror will go, check the edges and corners, and cut to the template. It feels slow. It is much faster than re-cutting glass. If you are ordering an LED mirror, do this measuring together with the electrical layout — our guide to what to know before you order an LED mirror covers where the power and controls need to land.

Edges, safety, and one last walk-through

Decide the edge before you finalize size: a polished flat edge, a bevel, or a framed finish all change how a tight fit looks. Bathroom mirrors should be safety-backed so that if the glass ever breaks, the pieces stay largely in place. Before you send numbers in, do one last walk-through with your tape marks still on the wall: stand at each sink, check eye level, confirm outlet positions, open every nearby door, and photograph the taped outline. Send us that photo with your numbers. The best order is the one that arrives right because the measuring was right.