Glass · Structural
Glass thickness calculator for wind load
A glass pane under wind load is checked twice: bending stress and deflection. For a rectangular pane supported on four edges, stress is σ = β·q·b²/t² and deflection is w = α·q·b⁴/D, where b is the short span and t the thickness. The pane passes when σ stays below the design strength of that glass type and w below the agreed limit.
Show the working
Show the working
Show the working
Show the working
See this pane bend in the wind lab →
Everything is computed in your browser — no upload, no sign-up, nothing about your project leaves your machine. Every coefficient and every standard used is written out below, so you can check the result instead of trusting it.
Glass thickness chart for wind load
The thinnest monolithic glass that passes both checks — bending stress, and deflection within short span / 65 — for common pane sizes supported on four edges. Read across to your design pressure. These are the calculator's own numbers, produced by the same code: a 1200 × 2200 mm pane at 1.2 kN/m² needs 6 mm fully tempered, or 8 mm annealed.
Fully tempered (toughened), mm
| Pane, mm (in) | 0.8 kN/m² 17 psf | 1.2 kN/m² 25 psf | 1.6 kN/m² 33 psf | 2.0 kN/m² 42 psf | 2.4 kN/m² 50 psf |
|---|---|---|---|---|---|
| 600 × 900 (24 × 35) | 3 | 3 | 4 | 4 | 4 |
| 900 × 1200 (35 × 47) | 4 | 4 | 5 | 5 | 5 |
| 1000 × 1500 (39 × 59) | 5 | 5 | 6 | 6 | 6 |
| 1200 × 1800 (47 × 71) | 5 | 6 | 8 | 8 | 8 |
| 1200 × 2200 (47 × 87) | 6 | 6 | 8 | 8 | 8 |
| 1500 × 2000 (59 × 79) | 6 | 8 | 8 | 8 | 10 |
| 1800 × 2400 (71 × 94) | 8 | 8 | 10 | 10 | 10 |
| 2000 × 3000 (79 × 118) | 10 | 10 | 12 | 12 | 12 |
Annealed float, mm
| Pane, mm (in) | 0.8 kN/m² 17 psf | 1.2 kN/m² 25 psf | 1.6 kN/m² 33 psf | 2.0 kN/m² 42 psf | 2.4 kN/m² 50 psf |
|---|---|---|---|---|---|
| 600 × 900 (24 × 35) | 3 | 3 | 4 | 4 | 5 |
| 900 × 1200 (35 × 47) | 4 | 5 | 5 | 6 | 6 |
| 1000 × 1500 (39 × 59) | 5 | 5 | 6 | 8 | 8 |
| 1200 × 1800 (47 × 71) | 5 | 6 | 8 | 8 | 10 |
| 1200 × 2200 (47 × 87) | 6 | 8 | 8 | 10 | 10 |
| 1500 × 2000 (59 × 79) | 6 | 8 | 8 | 10 | 10 |
| 1800 × 2400 (71 × 94) | 8 | 10 | 10 | 12 | 12 |
| 2000 × 3000 (79 × 118) | 10 | 10 | 12 | 15 | 15 |
Laminated glass, another deflection limit or a size that is not here: type it in above. For a whole facade, the schedule checker does every pane in one paste and groups them into the fewest make-ups.
How this is calculated
Small-deflection (linear) plate theory for a rectangular plate under uniform pressure, simply supported on all four edges — the classical Timoshenko solution. b is always the short span.
α and β depend only on the aspect ratio r = long span / short span. Values are interpolated between the tabulated points:
| r = a/b | 1.0 | 1.2 | 1.4 | 1.6 | 1.8 | 2.0 | 3.0 | ≥5.0 |
|---|---|---|---|---|---|---|---|---|
| α (deflection) | 0.00406 | 0.00564 | 0.00705 | 0.00830 | 0.00931 | 0.01013 | 0.01223 | 0.01302 |
| β (stress) | 0.2874 | 0.3762 | 0.4530 | 0.5172 | 0.5688 | 0.6102 | 0.7134 | 0.7500 |
Where we are being straight with you: those tabulated coefficients are the classical ones, computed for Poisson's ratio ν = 0.3, while glass is nearer 0.23. We use 0.23 in the rigidity D and the 0.3 coefficients in the table. For pre-dimensioning the difference is a few per cent and it errs on the safe side for deflection. We would rather tell you than hide it.
Design strength
Design bending strength follows the form used in EN 16612:
| Glass type | f_bk | Design strength under wind |
|---|---|---|
| Annealed float (EN 572) | 45 N/mm² | 25.0 N/mm² |
| Heat-strengthened (EN 1863) | 70 N/mm² | 45.8 N/mm² |
| Fully tempered (EN 12150) | 120 N/mm² | 87.5 N/mm² |
Laminated glass
A laminated pane sits somewhere between two loose plies and one solid pane, depending on how much shear the interlayer transfers — which changes with temperature and how long the load lasts. Rather than pick a number for you, this page computes both bounds and takes the conservative one for the verdict:
The real value lies between them. EN 16613 and the Wölfel–Bennison method give it from the interlayer's shear modulus at the design temperature and load duration. A stiff ionoplast interlayer on a cold day approaches the upper bound; a soft PVB on a hot day approaches the lower one. Nominal thicknesses are used throughout — real glass is thinner than nominal, which is another small margin on the safe side.
What this page does not do
- It does not compute wind pressure. You supply the already-factored design pressure from EN 1991-1-4 or ASCE 7.
- Four-edge support only. Two edges, three edges, point fixings and structural silicone are different calculations and will give different answers.
- Single pane only. In an insulating glass unit the two panes share the load through the gas cavity; that sharing is not modelled here.
- Linear theory. Once deflection passes roughly half the thickness, membrane action kicks in and the real pane is stiffer and less stressed than this calculation says. You get a warning when that happens.
- No safety, containment or post-breakage checks, no thermal stress, no barrier or impact loading.
Worked example you can check by hand
A 1200 × 2200 mm pane, 10 mm fully tempered, under 1.20 kN/m².
b = 1200 mm, a = 2200 mm, r = 1.8333 → interpolating between the 1.8 and 1.9 columns, α = 0.009453 and β = 0.5762. q = 1.20 kN/m² = 0.0012 N/mm².
Type those numbers into the calculator above and you should get exactly these figures — including the 21%, which is the deflection check and not the stress one. On toughened glass that is the usual outcome: the pane is nowhere near breaking and the thing that decides its thickness is how much it bends. If you ever find the calculator disagrees with this worked example, the calculator is wrong and we want to know.