Best Perspex Thickness for Boat Windscreens (Size Chart)
"What thickness perspex do I need for my boat windscreen?" is one of the most common questions we get at EXP Plastics. Get it wrong and your windscreen will flex, distort or crack the first time you hit rough water — get it right and it will outlast the rest of the boat.
Here's the guide our marine fabrication team uses when specifying replacement windscreens.
Why perspex thickness matters
A boat windscreen has to survive three things at once:
- Wind load — a flat 6mm panel that's fine at 20 knots will flex noticeably at 40.
- Wave impact — a solid green wave over the bow puts enormous point-load on the glazing.
- UV degradation — thinner sheets lose stiffness faster as they age. A little extra thickness buys you years of service life.
Thickness also drives what fabrication techniques are possible. Cold-formed curves need thinner material; thermoformed windscreens need 6mm or heavier to hold their shape.
Perspex thickness chart by boat type
| Boat type | Length | Recommended thickness |
|---|---|---|
| Tinnies, dinghies, small runabouts | Under 4.5m | 4mm cast acrylic |
| Runabouts, bow riders, small centre consoles | 4.5–6m | 6mm cast acrylic |
| Cabin cruisers, sailing yachts, half-cabins | 6–9m | 8–10mm cast acrylic |
| Offshore, commercial, charter vessels | 9m+ | 10–15mm acrylic, or polycarbonate |
| Portlights, small cabin ports | Any | 5–6mm tinted acrylic |
These are starting points — always match or exceed the thickness of the original panel unless a fabricator advises otherwise.
Flat vs curved windscreens
Flat panels can be cut and fitted straight from sheet stock. Curved windscreens need to be thermoformed — the perspex is heated in an oven, pulled over a mould and cooled to lock in the shape. Thermoforming requires 6mm or heavier so the panel holds its curve, and cast acrylic (not extruded) so the finish stays optically clear.
Tinted vs clear
Grey and bronze tints reduce glare and cabin heat — a genuine safety benefit on long offshore days. Tinted perspex has the same structural properties as clear, so thickness recommendations don't change. Ask us for Grey 2074 or Bronze 2404 in the same thickness as your original.
When to consider polycarbonate instead
If your windscreen is more than about 1.2m across, exposed to regular wave impact, or fitted to a commercial vessel, polycarbonate at the same thickness will give you 200×+ the impact resistance. Read our full marine polycarbonate vs glass comparison for details.
Get your windscreen specified and cut on the Gold Coast
Bring in your old windscreen (or a template) and we'll match the material, thickness and tint exactly. Call 07 5620 1038, browse acrylic Perspex stock or head to our boat & marine components page.
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