Glass Thickness Guide: 4mm to 15mm
Ordering too thin for the span is the most common specification mistake we see. This is a quick reference for what each weight is actually for.
The question that decides it
Not “how big is the panel” but “how far between the supports, and what is pressing on it”.
A 1500mm pane held in a frame on all four edges is a straightforward job for 4mm. The same 1500mm as an unsupported shelf span is a different problem entirely.
Thickness by application
4mm — window glazing, picture frames, cabinet door glass, small internal panels, wardrobe mirrors. The most common replacement weight in older homes. About 10kg per square metre.
5mm — larger window panes and internal doors, where 4mm would flex. Common in patterned glass for door panels. About 12.5kg per m².
6mm — the all-rounder. Shelving on short spans, cabinet doors, standard glazing, framed shower screens, louvre blades, larger wall mirrors. About 15kg per m².
8mm — larger shelves, protective table covers, heavier glazing. About 20kg per m².
10mm — frameless shower screens, table tops on a solid base, long shelf spans, structural panels. About 25kg per m².
12mm — dining tables, large frameless screens, balustrade infills, wide shelf spans. About 30kg per m².
15mm — large dining tables, wide spans, and where the substantial look of a thick polished edge is the point. About 37.5kg per m².
Weight is not a footnote
Those figures add up faster than people expect. A 2000 × 900mm panel in 12mm is about 54kg — genuinely a two-person lift, and awkward because it is large as well as heavy.
Check three things before ordering anything thick: can you carry it, will the fixings hold it, and will it come through the door. Glass cannot be trimmed on site.
What pushes you thicker
- Longer unsupported span — the main factor
- Point supports rather than continuous — pins and pegs concentrate stress; channels and rails spread it
- Deeper shelves — more leverage on the same span
- Heavier or concentrated loads — books and plates are much heavier than they look
- Cantilevered panels — supported on one edge only, these want engineering rather than a rule of thumb
Thickness is not safety
Worth being explicit. A thicker pane of ordinary annealed glass is still ordinary annealed glass — it breaks into the same long sharp shards, just larger ones.
If the position requires safety glass, it requires toughening or laminating, and no thickness substitutes for that. See when safety glass is required.
Matching an existing pane
Measure the edge of a broken piece with a ruler, or check the depth of the frame rebate. Getting this wrong in either direction causes problems: too thin and the pane rattles in the frame, too thick and it will not seat.
Related reading
- Shelves — span-by-span guidance
- Table tops — thickness, overhang and corner radius
- Shower screens — framed, semi-frameless and frameless
Not sure? Email the dimensions and what the panel is for to info@affordableglassonline.com.au. Advice at this stage costs nothing and a remake costs a good deal.