Marine plywood sizes and thickness: sheet sizes, mm and inches

What sizes does marine plywood come in?

Marine plywood comes in four main sheet sizes: 2440 × 1220 mm, 2500 × 1220 mm, 3100 × 1530 mm and 3100 × 1830 mm. The first is the 8 × 4 ft sheet sold by most timber merchants; the others are the okoume mill formats boat builders buy to reduce joins.

The sheet size is not fixed by the BS 1088 standard. BS 1088 sets the tolerance: a sheet may be up to 6.3 mm over its stated length or width, never under. That is why one mill’s 2440 × 1220 mm sheet can measure a few millimetres more than another’s.

What are the standard marine plywood thicknesses in mm?

Standard marine plywood thicknesses are 4, 6, 9, 12, 15, 18, 22 and 25 mm, the sizes listed in the BS 1088 tolerance table. Stockists in the UK and Europe usually hold 6, 9, 12, 18 and 25 mm, and order the rest from the mill.

Tolerances are from BS 1088, the British Standard for marine plywood (BSI listing read 20 October 2026). The bias is toward undersize: an 18 mm sheet may be 17.02 mm thick but never more than 18.12 mm.

How do marine plywood thicknesses convert to inches?

Marine plywood in inch markets is sold by fraction and in metric markets by millimetre; the nearest pairs are 1/4 inch to 6 mm, 3/8 to 9 mm, 1/2 to 12 mm, 5/8 to 15 mm, 3/4 to 18 mm and 1 inch to 25 mm. The inch sizes are slightly thicker, because 1 inch is exactly 25.4 mm (NIST).

A plan drawn in inches and built in metric sheets loses up to 1.1 mm per panel at 3/4 inch to 18 mm. Check rebates, slot widths and fastener lengths before cutting. More conversions are in the plywood thickness guide.

What size is 18 mm marine plywood?

18 mm marine plywood is sold as 2440 × 1220 mm sheets in most markets and as 2500 × 1220 mm in okoume from European mills. It is the most bought marine thickness because it serves decks, cabin floors, docks and heavy bulkheads.

• Thickness range under BS 1088: 17.02–18.12 mm.
• Sheet: 2440 × 1220 mm, 2.98 m² of panel.
• Inch equivalent: 3/4 inch is 19.05 mm, so 18 mm is just under.
• Face veneers: 1.3–3.8 mm each under BS 1088, with core veneers no thicker than 4.8 mm, so marine panels carry fewer, thicker plies than furniture plywood.

Wider beam spacing or heavy loads call for 22 or 25 mm, as the boat’s designer specifies. See plywood for boat floors and decks.

What size is 9 mm and 12 mm marine plywood?

9 mm and 12 mm marine plywood are both standard in 2440 × 1220 mm and 2500 × 1220 mm sheets. They are the workhorse sizes for boat interiors.

• 9 mm (3/8 inch): bulkheads in small craft, hull sides of stitch-and-glue dinghies, lockers and berths. BS 1088 range 8.25–9.06 mm.
• 12 mm (1/2 inch): cabin soles, structural bulkheads, transom doublers and dinghy decks. BS 1088 range 11.18–12.09 mm.

Both bend well enough for gentle curves along the length of the sheet. For tight curves, builders drop to 6 mm or laminate two thinner sheets.

What is the thickest marine plywood you can buy?

25 mm is the thickest marine plywood most stockists carry. Okoume mills in France and Italy make panels from 3 mm up to 40 mm to order, and 30 mm panels are sold for engine beds and heavy transoms.

When a design calls for more than 25 mm, boat builders usually laminate two thinner sheets with epoxy, for example 2 × 18 mm for a 36 mm transom. Lamination lets each sheet be inspected, and the glue line adds stiffness. Order the thickness that the design specifies, and measure it: a 25 mm BS 1088 sheet may run down to 23.84 mm.

What marine plywood sizes are sold in the Philippines?

Marine plywood in the Philippines is sold as 4 × 8 ft sheets, 1220 × 2440 mm, in 1/4, 3/8, 1/2 and 3/4 inch. Builders and hardware stores call them by the inch and use them for roofing boards, formwork, wet-area cabinets and boats. Shelf prices run from about ₱495 for a 1/4 inch sheet to about ₱1,365 for a 3/4 inch sheet.

Prices come from LPM Express, a Philippine online hardware store that sells Richmond marine plywood in 1/4, 1/2 and 3/4 inch with same-day Metro Manila dispatch. An NCR formwork price list put 3/4 inch marine at ₱1,374; both sources were read in October 2026 and prices change by store and brand. Many sheets sold as “marine” in the Philippines are moisture-resistant panels rather than boil-proof BS 1088, so ask for the glue class and the measured thickness. Moisture-resistant general-purpose plywood belongs to BS EN 636, which covers plywood for dry, humid or exterior conditions.

An importer ordering by the container works differently: a 40HC holds up to 990 sheets of 18 mm on a Styrax core in the 1220 × 2440 mm size, and the voyage from Hai Phong to the Philippines is 5–12 days at sea. Quote CIF Manila per m³, then divide by the sheet volumes below to compare with the shelf price.

The inch label is a trade name. A “1/2 inch” sheet in local hardware stores is often 11–12 mm actual, and a “3/4 inch” sheet 17–18 mm. Ask for the measured thickness when the panel must fit a frame. The same 4 × 8 ft sheet is the standard for every plywood type sold there.

What marine plywood sizes are sold in Australia, the UK and the Middle East?

Each market keeps its own sheet: 2400 × 1200 mm in Australia and New Zealand, 2440 × 1220 mm in the UK, Ireland and the Gulf, and 2500 × 1220 mm where okoume from European mills dominates.

• Australia and New Zealand: marine plywood to AS/NZS 2272, mainly 2400 × 1200 mm, with longer lengths from specialist suppliers. Thicknesses 4 to 25 mm.
• UK and Ireland: BS 1088 in 2440 × 1220 mm, most often 6, 9, 12, 18 and 25 mm.
• Cyprus, Dubai and Abu Dhabi: imported BS 1088 hardwood and okoume panels in 2440 × 1220 and 2500 × 1220 mm.

For importers who sell into several markets, the 2440 × 1220 mm sheet travels best: it is the default press size of Asian mills and fills a 40HC well.

What are jumbo marine plywood sizes used for?

Jumbo marine plywood, 3100 × 1530 mm and 3100 × 1830 mm, is used for hull panels, decks and large bulkheads where a standard sheet would need a join. A 3100 × 1830 mm sheet covers 5.67 m², about 1.9 times a 2440 × 1220 mm sheet.

Jumbo sheets cost more per square metre and need two people or a vacuum lifter to handle. They pay back on hulls longer than 2.4 m, where each scarf joint avoided saves glue, fairing and time. For panels longer than 3100 mm, builders scarf two sheets at a slope of 8:1 to 12:1.

What does marine plywood thickness mean for weight and handling?

Sheet weight rises with thickness at the same species: an 18 mm sheet weighs three times a 6 mm sheet of the same timber. Okoume marine plywood is the lightest common choice; tropical hardwood BS 1088 panels are heavier and stiffer.

Weights use 550 kg/m³ for light okoume and 650 kg/m³ for dense tropical hardwood; multiply the volume by the density on the supplier’s data sheet for the exact figure. For boat building, ask for the weight per sheet: it drives the boat’s displacement as much as the strength.

What thickness of marine plywood for each boat part?

Marine plywood thickness follows the part: 4–6 mm for skins and linings, 9–12 mm for bulkheads and soles, 18–25 mm for decks under heavy load, transoms and stringers. The table gives the usual starting point on dinghies and small day boats; the boat’s plans always decide.

Two rules keep the numbers honest. First, thickness is only half the stiffness: the frame or beam spacing under the panel counts as much. Second, every exposed edge and fastener hole is sealed with epoxy, whatever the thickness, because water enters through the end grain. For the hull, deck and transom builds in full, read marine plywood for boat building.

How do you choose the right marine plywood size?

Choose the marine plywood size from the largest panel you need, then the thickness from the load and the frame spacing.

1. Measure the largest part and compare it with 2440 × 1220, 2500 × 1220 and 3100 × 1530 mm sheets.
2. Count joins: if a standard sheet needs a scarf joint, price a jumbo sheet against the extra work.
3. Set the thickness from the design or the frame and beam spacing.
4. Check the tolerance: design rebates for the undersize BS 1088 allows.
5. Specify the grade and standard: BS 1088, or AS/NZS 2272 in Australia, written on the order.

The marine plywood buying guide covers grades, glue and how to identify real marine panels.

Which plywood sizes suit outdoor jobs that do not need BS 1088?

Outdoor joinery, stair treads, wall sheathing and covered boat-shed fittings use exterior plywood with a phenolic WBP bond in the same 1220 × 2440 mm sheets. These jobs need a water-resistant glue line, not the face and veneer rules of BS 1088.

Minh Thanh Plywood makes exterior plywood with phenolic WBP bond in 1220 × 2440 and 1250 × 2500 mm sheets, 3–40 mm thick, with utility C/D faces, and supplies origin records and geolocation files with EU orders. Sizes such as 1220 × 2500 and 1220 × 2280 mm are made to order. See exterior plywood for the build.

What this means for your order

Write the size on the order as sheet length × width × thickness in millimetres, then the standard and the grade.

• Sheet: 2440 × 1220 mm, 2500 × 1220 mm or a jumbo format.
• Thickness: in millimetres, with the inch size it replaces if the plans are imperial.
• Standard: BS 1088 for boats, AS/NZS 2272 in Australia, or exterior WBP plywood where marine rules are not needed.
• Face and core: species, for example okoume or a tropical hardwood.
• Quantity: sheets per thickness and packing.

For exterior plywood, Minh Thanh’s minimum is one 40HC with mixed thicknesses by agreement, production takes 15–45 days after the deposit, and free samples come with the quotation. Spec line: exterior plywood, phenolic WBP bond, C/D faces, 1220 × 2440 × 18 mm, 1×40HC. Send it to [email protected].