How to Measure for a Cut to Size Mirror
Mirrors are more forgiving than window glass because most are fixed to a flat wall rather than into a frame. The mistakes are different, and they are mostly about what happens around the edges.
Decide the finished size first
Unlike a replacement pane, you are usually choosing the size rather than matching one. Mark the intended outline on the wall with masking tape and live with it for a day. Mirrors almost always look larger installed than they do on paper.
For a bathroom mirror above a vanity, a common approach is to match the vanity width or come in slightly narrower on each side. Going wider than the vanity tends to look accidental.
Watch what sits around it
Measure the clear wall area, not the wall. Power points, light switches, shaver outlets, tiles that stop partway up, cornices and skirting all reduce the space you actually have.
Leave a deliberate gap rather than butting the mirror against something. A mirror finishing 5mm short of a tile edge looks intentional; one touching it looks like it did not fit.
Choose the thickness
Two weights cover almost everything:
- 4mm — small panels, wardrobe doors, anything up to roughly a metre square.
- 6mm — larger wall mirrors, and anywhere rigidity matters.
The reason to go to 6mm on a large mirror is distortion. A big 4mm sheet follows any unevenness in the wall behind it, and a slightly bowed wall produces a visible warp in the reflection. If the wall is old plaster or the mirror is over about 1200mm in either direction, use 6mm.
Our full range is on the mirrors page, including bronze and dark grey tints for feature panels.
Order polished edges
Any mirror that will not sit inside a frame needs polished edges. An unpolished cut edge is sharp, it looks unfinished, and on a mirror it is right at eye level where nobody can miss it.
This is the single most common regret we hear about. If in doubt, choose polished — read the edge finish guide if you want the detail.
Think about how it is fixed
How you plan to mount it changes what you order:
- Mirror adhesive — nothing extra needed, but the wall must be flat and sound. Use adhesive made for mirrors; ordinary construction adhesive can attack the silver backing and cause black edges over time.
- Clips or J-channel — allow for the clip depth, and remember the bottom clips will cover a few millimetres of the mirror face.
- Drilled holes for screws or standoffs — holes must be specified and drilled before the mirror is toughened or coated. They cannot be added afterwards. Send us a drawing with hole positions and diameters.
Get it through the door
Worth checking before you order, not after. A 2000 × 900mm mirror will not go round a tight stair landing, and glass cannot be trimmed on site. Measure the narrowest point of the route in — doorways, corners, stairwells — and tell us if access is difficult.
What to send us
- Width and height in millimetres
- Thickness (4mm or 6mm)
- Edge finish — almost always polished
- Any holes or cutouts, with a dimensioned sketch
- A photo of the space if anything is unusual
Enter your sizes on any mirror product for an immediate price, or email us at info@affordableglassonline.com.au if you would rather talk it through.