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 →
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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, for a 10-minute wind (k_mod 0.74): 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 | 4 | 4 | 5 | 5 |
| 900 × 1200 (35 × 47) | 4 | 5 | 6 | 8 | 8 |
| 1000 × 1500 (39 × 59) | 5 | 6 | 8 | 8 | 8 |
| 1200 × 1800 (47 × 71) | 6 | 8 | 8 | 10 | 10 |
| 1200 × 2200 (47 × 87) | 6 | 8 | 10 | 10 | 12 |
| 1500 × 2000 (59 × 79) | 8 | 8 | 10 | 12 | 12 |
| 1800 × 2400 (71 × 94) | 8 | 10 | 12 | 15 | 15 |
| 2000 × 3000 (79 × 118) | 10 | 12 | 15 | 15 | 19 |
Laminated glass, another deflection limit, the 5-second gust 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. The deflection coefficient α does not depend on ν, so the deflection is unaffected; the stress coefficient β does, and with 0.3 the stress comes out up to 5.7 % high for a square pane (1.2 % at 2:1, nothing from 5:1), which is on the safe side. We would rather tell you than hide it.
Design strength
Design bending strength follows the form used in EN 16612:
How long the load lasts matters: glass is weaker under a long load than under a short one. Many standards and national annexes take 10 minutes for wind, and that is what the calculator uses unless you choose the 5-second gust; check which one the standard that applies in your country asks for. kmod is the same formula as in the balustrade calculator.
| Glass type | f_bk | Design strength, 10-minute wind (k_mod 0.74) | Design strength, 5-second gust (k_mod 1.00) |
|---|---|---|---|
| Annealed float (EN 572) | 45 N/mm² | 18.5 N/mm² | 25.0 N/mm² |
| Heat-strengthened (EN 1863) | 70 N/mm² | 39.4 N/mm² | 45.8 N/mm² |
| Fully tempered (EN 12150) | 120 N/mm² | 81.0 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 can be slightly thinner within its manufacturing tolerance, which raises stress and deflection a little: it works against you, not for you, so leave some headroom when the utilisation gets close to 100 %.
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.
See it in use, in 27 seconds
Pane size and wind pressure, and the page says whether it passes on stress and on deflection to EN 16612. A recording of the tool as it is, no voice.
Questions people ask
- How do you calculate glass thickness for wind load?
- A pane under wind load is checked twice. For a rectangular pane supported on four edges, bending stress is σ = β·q·b²/t² and deflection is w = α·q·b⁴/D, where q is the design wind pressure, b the short span, t the thickness and β, α depend on the aspect ratio. The thickness passes when σ stays below the design strength of that glass type and w below the agreed deflection limit.
- What is the deflection limit for glass under wind load?
- EN 16612 sets no deflection limit. It is a project or national requirement, so check the one that applies to you; the calculator lets you choose it and shows which check governs, stress or deflection.
- How do you calculate glass deflection under wind load?
- For a pane supported on four edges, the centre deflection is w = α·q·b⁴/D, with D = E·t³/(12·(1 − ν²)), E = 70 000 N/mm² and ν = 0.23. The pane this page opens with, 1200 × 2200 mm of 10 mm fully tempered glass under 1.20 kN/m², deflects 3.82 mm at the centre: 21 % of the short span / 65 limit of 18.46 mm, while its bending stress uses 12 % of the design strength for a 10-minute wind. Deflection, not stress, decides its thickness.