A custom mirror only works if the measurements are right. Order it a touch too big and it will not fit the space; order it too small and it looks lost on the wall. The measuring itself is straightforward as long as you do it methodically and know whether you are sizing a mirror to hang on a wall or one that has to fit inside a frame or recess, because those are measured differently. Here is how to take the measurements properly, what else you need to specify when you order, and when it is worth having the mirror templated for you.
What you need before you start
Keep it simple: a steel tape measure, a pencil and paper, a level, and a second pair of hands for anything large. Before you measure, decide which kind of job you have. A wall-mounted mirror is one where you choose the finished size you want to see on the wall. A mirror that fits into a frame, an alcove or a recess is one where the opening dictates the size and you measure that opening. Getting clear on which of the two you are doing first saves the most common mistake, measuring for one and ordering as if it were the other.
Measuring a wall-mounted mirror
For a mirror that simply hangs on the wall, you are choosing its finished dimensions. Measure the available wall space in both directions, then decide how much of it you want the mirror to fill, leaving sensible clearance around light fixtures, outlets, switches, a backsplash or any trim. Over a vanity, a common approach is to make the mirror a little narrower than the vanity and centre it, though that is a matter of taste. Give some thought to height and eye level as well, which our guide to mirror placement covers in more detail. Write the size down as width by height and label which is which so there is no confusion on the order.
Measuring for a frame, recess or alcove
When the mirror has to fit into an opening, accuracy matters more, because walls and openings are rarely perfectly square. Measure the opening in three places across, at the top, middle and bottom, and three places down, at the left, middle and right. Use the smallest measurement in each direction as your starting point, then subtract a small clearance so the mirror slides in without binding rather than jamming or cracking. The exact clearance to allow depends on how it is being fitted, so confirm the tolerance with your supplier before you finalize the size. Never assume an opening is square; the three-point measurement is what catches the wall that is out by a few millimetres.
What else to specify when you order
The size is only part of the order. A few other details decide whether the mirror is right:
Thickness. Around 4 mm suits smaller mirrors, while larger ones are usually 6 mm so they stay flat and rigid rather than rippling the reflection.
Edge finish. A flat-polished edge is clean and modern; a bevelled edge adds a framed, decorative line, and the bevel width is part of the look, as we explain in our guide to bevelled mirrors.
Cutouts and notches. If the mirror has to clear sconces, outlets or switches, give the size and position of each, measured from the edges.
Shape and mounting. Rectangular is standard; arches and custom shapes need a template, and telling the supplier how it will mount, clips, a cleat or adhesive, lets them finish the edges to suit.
The bevelled-edge option in particular changes the character of a mirror, and it is worth seeing what it does before you decide, which is the point of our piece on bevelled mirrors. Note your chosen edge finish clearly on the order.
Tips that prevent expensive mistakes
Measure twice, work in consistent units, ideally millimetres, and always state width first and then height, or label each, so the mirror is not made rotated. Photograph the space with the measurements noted on the picture. For an irregular wall, a tricky alcove, or anything with cutouts or an unusual shape, a paper or cardboard template, or an on-site measure, removes the guesswork entirely. Many glass shops will template or measure for you, which is the surest way to get a piece that fits the first time.
When to have it measured and fitted for you
Some mirrors are worth handing over from the start. Large, heavy pieces, tricky alcoves, anything needing cutouts, and custom shapes all benefit from a professional measure and installation, both because the measurement is less forgiving and because mirror glass is heavy and needs secure mounting to stay safely on the wall. It is the kind of thing the team handles as part of residential glass work. A measured-and-fitted mirror takes the risk out of an expensive custom piece.
FAQs
Ready to get help with your glass issue?
Planning a custom mirror and want it measured and fitted right? Request a free quote. The team handles custom mirrors and residential glass across Alberta. Call 310-GLAS (4527), text 780-652-1296, or book online.