Glass Thickness Guide: 4mm to 15mm
Quick answer: 4mm for picture frames and small panes, 5–6mm for most windows and cabinet doors, 8mm for larger shelves, 10mm toughened for frameless shower screens and table tops, 12mm for dining tables and wide spans. Glass weighs about 2.5 kg per m² for every millimetre of thickness. A 600 × 900mm clear panel with polished edges costs $142.00 in 4mm and $212.86 in 10mm, delivered across Melbourne, inner Geelong and Sydney.
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.
Key numbers
- Float glass weighs about 2.5 kg per m² for every millimetre of thickness: 4mm ≈ 10 kg/m², 6mm ≈ 15 kg/m², 10mm ≈ 25 kg/m², 12mm ≈ 30 kg/m².
- A 600 × 900 mm clear panel costs $142.00 in 4mm, $152.80 in 6mm, $212.86 in 10mm and $233.38 in 12mm.
Prices are from our online calculator, rectangular panels with polished edges, delivery across Melbourne metro and inner Geelong included. Prices checked October 2026.
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.
Common questions
What thickness glass do I need for a shelf?
For a shelf supported at both ends with a normal load: up to 400mm span, 6mm; 400 to 700mm, 8mm; 700 to 900mm, 10mm; over 900mm, 12mm and an extra support. Deep shelves, heavy loads and pin supports push you one size thicker.
What thickness is a glass table top?
6–8mm is enough for a protective cover over a solid table. A glass top that sits on a base by itself is usually 10mm toughened, and 12mm for large dining tables. Toughened is recommended for any table top.
What thickness is shower screen glass?
Frameless shower screens are 10mm toughened. Semi-frameless screens are usually 6–8mm toughened and framed screens 4–6mm toughened. Shower glass must be safety glass under AS 1288.
How heavy is glass?
About 2.5 kg per m² per millimetre: 4mm is about 10 kg/m², 6mm 15 kg/m², 10mm 25 kg/m² and 12mm 30 kg/m². A 2000 × 900mm panel in 12mm weighs about 54 kg.
Is thicker glass the same as safety glass?
No. Thicker annealed glass still breaks into sharp shards. Where safety glass is required, it must be toughened or laminated, whatever the thickness.