Glass · Ordering
Glass cut to size: how to measure it, choose it and order it
To order glass cut to size, give the glass shop the finished width and height, the thickness, the type of glass and the edge finish, plus a sketch of any holes or notches. Measure the space the glass goes into, not the old piece. Work the thickness out from what the glass has to carry: a table top, a shelf and a window pane are three different calculations. And order toughened glass finished, because once it is toughened it cannot be cut, drilled or ground.
Six steps from the tape measure to the order
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Measure the space, not the old glass
For a window or a door, measure the opening between the rebates: three widths, three heights, the smallest of each, and both diagonals. The glass is then made a few millimetres smaller so it can be packed and sealed, and the full method is in how to measure an opening for glass.
For furniture (a table top, a shelf, a cabinet door) the size is the size you want, so decide first what the glass rests on. That decision changes the thickness.
Width × height, in millimetres, and say which one is the width.
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Work out the thickness from the load
A table top carries what is put on it, a shelf carries books and the odd heavy object, a window carries wind. The table top and shelf calculator checks a spread load and a point load (something heavy on a small foot), for stress and for sag, and gives the thinnest stock thickness that passes both. For a window pane, the wind load calculator does the same against the wind pressure of the site.
How it is supported matters as much as its size: a top held on all four edges sags far less than a shelf resting only on its two ends.
Habit is not a thickness. The two examples below come out at different thicknesses for very similar sizes.
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Toughened, laminated or plain float
Anything people lean on, put things on or walk past should be toughened or laminated. Plain annealed float breaks into long sharp blades. Toughened glass is several times stronger and breaks into small blunt pieces. Laminated glass may crack, but it stays in one piece, held by the interlayer.
Toughening is done after cutting. Every cut, hole, notch and edge has to be finished before the glass goes into the furnace, and none of it can be changed afterwards: a toughened pane that comes out 3 mm too big is a new pane. If you are not sure what a pane you already have is, see is this glass toughened or annealed?
Near doors and low down, safety glass may be required by the building rules where you are. Ask the glass shop before choosing.
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Edges, holes and notches
A freshly cut edge is sharp. Where the edge can be seen or touched, ask for a polished edge; where it disappears into a frame or a channel, an arrised (lightly ground) edge is enough. Say which edges, if not all four.
Draw holes and notches on a sketch, each one dimensioned from the same named corner, with its diameter or size. The glass shop sets the minimum distance from an edge and between holes for each thickness, so check with them before designing round a fitting.
One sketch with dimensions from one corner saves more mistakes than a paragraph of description.
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Weight, and how it gets there
Glass weighs 2.5 kg/m² for every millimetre of thickness. The glass weight calculator works it out for any pane and says how many people it takes to carry it by the usual 25 kg guideline.
A large top or a full-height panel can be heavier than it looks. Think about stairs, doorways and who will be there to lift it.
Delivery or collection goes on the order too.
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What goes on the order
Quantity; width × height in mm; thickness; type (toughened, laminated, float) and any tint or low iron; edge finish and which edges; corners square or radiused; the sketch of holes and notches; delivery or collection.
Keep a copy with the measurements you took. If something does not fit, they show whether it was the measurement or the cutting.
One line per piece, with a reference (G01, G02…) that also goes on the sketch.
Worked example: a table top on a frame
A top of 1200 × 700 mm, resting on a frame that holds all four edges, in toughened glass. The loads are the calculator's starting values: 150 kg/m² spread over the top, and an object of 50 kg standing on a foot 300 mm wide, both permanent; the sag limit is the span over 100.
| Check | Calculator result |
|---|---|
| Thinnest stock thickness that passes | 8 mm |
| At 8 mm | Passes. Governed by deflection, at 70% of its limit. |
| Sag at 8 mm | 4.91 mm; limit 7.0 (span/100) · 70% |
| One size thinner, 6 mm | Does not pass. Over the limit on deflection — 166% of what is allowed. Thicker glass, a shorter span or another support. |
| One size thicker, 10 mm | Governed by deflection, at 36% of its limit. |
| Weight at 8 mm | 16.8 kg (20.0 kg/m²) |
| Handling | One person, by the 25 kg guideline |
So the order line reads: one piece, 1200 × 700 mm, 8 mm toughened, polished edges. The thinner glass fails on sag, not on strength, which is typical of a top that is large for its thickness.
Open the table top calculator Open the weight with these sizes
The table top calculator does not take sizes from a link: choose four edges and toughened, and type the width and length.
Worked example: a shelf resting on its two ends
A shelf of 900 × 300 mm sitting on supports at its two ends, so it spans 900 mm, in toughened glass, with the same starting loads.
| Check | Calculator result |
|---|---|
| Thinnest stock thickness that passes | 10 mm |
| At 10 mm | Passes. Governed by deflection, at 71% of its limit. |
| One size thinner, 8 mm | Does not pass. Over the limit on deflection — 139% of what is allowed. Thicker glass, a shorter span or another support. |
| One size thicker, 12 mm | Governed by deflection, at 41% of its limit. |
| Weight at 10 mm | 6.8 kg (25.0 kg/m²) |
A shelf with about a third of the table top's area needs thicker glass, because it is held on two edges instead of four.
Questions
Can toughened glass be cut to size after it is made?
No. Cutting, drilling, notching and edge work all have to be done before the glass is toughened; afterwards any of them shatters it. That is why toughened glass is ordered to the exact finished size.
What thickness of glass do I need for a table top?
It depends on the size, how it is supported and what it carries, so work it out rather than copy someone else's. In the worked example above, a 1200 × 700 mm top held on all four edges comes out at 8 mm toughened with the calculator's starting loads; held on two edges, or loaded more heavily, it needs more.
Do I give the glass shop the size of the opening or the size of the glass?
Either, as long as you say which. If you give the opening, the shop takes off the clearance; if you give the glass size, you have already taken it off. Taking it off twice is the commonest way to get a pane that is too small.
How heavy is a piece of glass?
2.5 kg per square metre for every millimetre of thickness: 8 mm glass is 20.0 kg/m². The weight calculator does it for any size, laminated and double glazing included.