Glass thickness depends on the size of the pane, how it is supported, the load it carries and the safety rules for its location. Sealed units in windows usually use panes between 3mm and 10mm, shelves and shower screens use thicker toughened glass, and laminates such as 6.4mm suit safety glazing. Balustrades, floors and other structural glass must be specified by calculation.
How is glass thickness described?
Glass is sold in nominal thicknesses measured in millimetres. Float glass, the flat glass that most other types start from, is made in standard thicknesses of 2, 3, 4, 5, 6, 8, 10, 12, 15, 19 and 25mm. Toughened glass is ordinary float glass that has been heat-treated, so it comes in the same thicknesses but is about four times stronger than the annealed glass it started as.
Laminated glass is described by its total thickness, including the plastic interlayer. A 6.4mm laminate is two 3mm panes bonded to an interlayer of about 0.4mm. A 6.8mm laminate uses the same two 3mm panes with a thicker interlayer of about 0.8mm. Thicker laminates, such as those used in balustrades, are built from toughened panes and are often described by their full make-up.
Thickness on its own does not make glass safe or strong enough. The type of glass, the way it is fixed, its size and the job it does matter just as much. A quote should state the thickness and the type, for example 10mm toughened or 6.4mm laminated, not just the thickness.
What thickness is used in windows and glazed doors?
Double-glazed units in homes usually use panes between 3mm and 10mm thick, often the same thickness on both sides. Thicker or laminated glass is used where the size of the pane, wind load, safety, security or noise reduction calls for it. In England, Approved Document L recognises that some of these needs require thicker glass, which affects how a unit's energy performance is shown.
Where glass is in a critical location, it must be safety glass or meet another route in the building regulations. In England, critical locations include glazing in doors up to 1500mm from the floor, side panels within 300mm of a door up to 1500mm, and other panels up to 800mm from the floor. Safety glass means toughened or laminated glass that meets the impact classes set out in Approved Document K.
Approved Document K also allows small panes of ordinary annealed glass in critical locations if they are at least 6mm thick and no larger than 0.5m², or 4mm thick in traditional leaded or copper lights where fire resistance is not a factor. Rules in Wales, Scotland and Northern Ireland follow similar principles but are set out in their own guidance.
What do 6.4mm and 6.8mm laminated glass mean?
These are the two laminates you will see most on window and door quotes. Both are made from two 3mm panes bonded to a plastic interlayer, usually PVB. If the glass is struck hard enough to break, the pieces stick to the interlayer, the pane cracks in a spider-web pattern and it usually stays in the frame. That makes laminated glass suitable for safety glazing and for windows and doors where keeping the opening closed after a break matters.
The difference is the interlayer: a 6.8mm laminate has a thicker one than 6.4mm. Do not choose a laminate on thickness alone. Laminated glass is classified by testing, for impact safety under BS EN 12600 and, for security glazing, for resistance to manual attack under BS EN 356. Ask which classification the glass has been tested to and whether it meets what your location or insurer requires.
Laminated glass can also include acoustic interlayers to reduce noise, or tinted and solar control interlayers. It can be used as one pane of a double-glazed unit, so a window can have laminated glass on the outside, the inside or both.
| Thickness | Typical type | Typical use |
|---|---|---|
| 3mm–10mm | Float, toughened or coated panes | Panes in double-glazed window and door units |
| 4mm | Annealed | Traditional leaded or copper lights |
| 6mm | Annealed or toughened | Small panes up to 0.5m²; light display shelves |
| 6.4mm or 6.8mm | Laminated (two 3mm panes) | Safety and security glazing in windows and doors |
| 8mm–10mm | Toughened | Home shelving; shower screens |
| 12mm | Toughened | Heavy-duty shelving; larger shower panels |
| 17.5mm and above | Laminated toughened | Frameless balustrades, designed by calculation |
What thickness do shelves, tabletops and splashbacks need?
Glass shelves are normally toughened, and the thickness follows the load. Trade guidance links 4mm to 6mm glass with light display cases and cabinets, 8mm and 10mm with home use such as books, toiletries and kitchenware, and 12mm or more with heavy commercial loads such as bar shelving. The span between supports and the type of bracket also matter, so the supplier should check the shelf against what it will hold.
Glass tabletops are usually toughened. The thickness depends on the size of the top and how it is supported: a top resting on a full frame needs less than one that sits on a few small pads or a central base. Edges should be ground or polished, and the corners radiused if people will brush past them.
Glass splashbacks are made from toughened glass and are often back-painted in a chosen colour. Because toughened glass cannot be cut or drilled after toughening, every socket cut-out and fixing hole must be measured and made before the glass is toughened. Follow the supplier's and hob manufacturer's guidance on any clearance needed behind gas burners.
What thickness are shower screens?
Shower screens and enclosure panels are made from toughened safety glass, because they are in a wet area where people may slip and fall against the glass. Fixed and frameless screens are commonly made in 8mm or 10mm toughened glass, and some larger panels use 12mm. Fixing channels and hinges are made to suit a particular glass thickness, so the glass and hardware must be specified together.
Framed enclosures can use thinner glass because the frame supports the edges, while frameless screens rely on the glass itself for stiffness and are fixed only at a wall channel, a floor channel or hinges. A wall-mounted support bar is often added to a tall fixed screen. All holes and notches for hinges and handles are cut before toughening, so accurate measuring of walls and tray levels is essential.
Weight is the other thing to plan for. The weight of glass rises in direct proportion to its thickness, so a large 10mm or 12mm panel is heavy to carry upstairs and puts real load on the wall fixings and hinges. Walls behind frameless screens need solid fixing points, which is worth checking before tiling, especially on stud or plasterboard walls.
What glass is used for balustrades and glass floors?
Glass in a balustrade is guarding, so it must resist the loads set for its location and behave safely if it breaks. Frameless balustrade systems clamp laminated toughened glass at the base, typically 17.5mm or more, and some base-channel systems are designed for glass from 12mm up to 21.5mm. Where single toughened panes are used, a handrail designed to stay in place if a panel breaks is normally needed.
Glass floors, stair treads and walk-on rooflights are made from toughened glass that is also laminated, so the glass keeps its integrity and stays in place if one layer is damaged. Each one is designed for its span, supports and use, and there is no standard thickness to pick from a list. The supporting frame or structure is designed at the same time as the glass.
The height, gap and load rules for balustrades differ between England, Wales, Scotland and Northern Ireland, and they also depend on whether the glass is inside a house, on a balcony or in a public building. The glass thickness follows from those rules and from the fixing system, so it is set by the system supplier or a structural engineer rather than chosen from a catalogue.
Why does structural glass need engineering?
Structural glass carries loads beyond its own weight, such as people leaning on a balustrade, walking on a floor or wind pressing on a large pane. Its thickness, make-up, supports and fixings have to be worked out by calculation, because glass gives no warning before it breaks and the consequences of a failure are serious. In England, Approved Document K sets loads for guarding by reference to BS EN 1991-1-1 and points to BS 6180 for barrier design.
Toughened glass can also break without an obvious impact, because of nickel sulphide inclusions formed during manufacture. Safety reports on glass failures have warned that glass which has not been properly heat-soaked is more likely to shatter in use. That is why structural designs usually rely on laminated glass that keeps its integrity after one pane breaks, and why heat-soak testing is often specified.
Engineered glass also sits outside some routine approval routes. Government guidance on competent person schemes for replacement windows and doors in non-domestic buildings excludes load-bearing structural glass, glazed curtain walling and revolving doors. For any structural glass, ask who has carried out the design calculations, what loads they cover and what the fixings are anchored into.
Frequently asked questions
Is thicker glass always stronger?
Thicker glass of the same type is stiffer and can span further or carry more load, but type matters as much as thickness. Toughened glass is about four times stronger than annealed glass of the same thickness, and laminated glass stays in place when broken. A thick annealed pane can still break into dangerous shards. Choose the type for the safety need first, then the thickness for the size and load.
Can toughened glass be cut or drilled?
No. Toughened glass must be cut to size and have all holes, notches and edge work done before it is toughened. Trying to cut or drill it afterwards makes it shatter. That is why toughened glass for splashbacks, shower screens, tabletops and doors is made to measure from accurate templates, and why a mistake in measuring usually means making a new panel.
What is the difference between toughened and laminated glass?
Toughened glass is heat-treated to make it about four times stronger than ordinary glass, and it breaks into small, blunt pieces. Laminated glass bonds two or more panes to a plastic interlayer, so when it breaks the pieces stay stuck together and the pane usually stays in place. Both can be safety glass. Laminated toughened glass combines the two and is used where glass must stay in place after breaking.
What thickness of glass do I need for a tabletop?
It depends on the size of the top and how it is supported. A top laid on a full frame or solid base needs less thickness than one resting on a few small pads or cantilevered from a central stand. Tabletops are normally toughened for safety, with polished edges and rounded corners. Give the supplier the size, the support details and the use so they can recommend a thickness.
Why does 6.4mm laminated glass appear on window quotes?
It is a common laminated safety glass made from two 3mm panes bonded to a thin plastic interlayer. It is often used in windows and doors for safety in critical locations, for security, or to hold the glass in place if it breaks. It can form one pane of a double-glazed unit. Check the impact classification on the quote rather than relying on the thickness.
Sources
- Approved Document K: protection from falling, collision and impact (GOV.UK)
- Approved Document N: glazing safety (GOV.WALES)
- Doors and windows: building regulations (Planning Portal)
- BS EN 356 Glass in building. Security glazing (BSI)
- Competent person schemes: current schemes (GOV.UK)
- CROSS safety report: toughened glass failures (Institution of Structural Engineers)
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