18 mm OSB board is the standard thickness for floor decks and heavy-duty roofs, made in 2440 × 1220 mm sheets and narrow tongue-and-groove (T&G) boards; 9 mm and 11 mm OSB sheets cover walls and hoarding. This guide gives OSB sizes, weights, grades and tolerances, and where an 18 mm plywood panel from Minh Thanh Plywood is the alternative.
What sizes and thicknesses does OSB board come in?
OSB board comes in full sheets of 2440 × 1220 mm (8 × 4 ft) and in narrower tongue-and-groove (T&G) boards for floors, in thicknesses from about 6 mm to 25 mm. The thicknesses most buyers order are 9 mm, 11 mm, 15 mm, 18 mm and 22 mm.
Oriented strand board (OSB) is made from wood strands laid in cross-oriented layers and pressed with resin. Because it is formed in a continuous press, producers can cut many sizes; the common ones are:
| Format | Size | Typical thicknesses | Main use |
|---|---|---|---|
| Full sheet, square edge | 2440 × 1220 mm | 9 mm, 11 mm, 15 mm, 18 mm | Walls, roofs, hoarding, packing |
| Full sheet, metric grid | 2397 × 1197 mm | 9 mm, 11 mm, 15 mm, 18 mm | Walls and roofs on a 1200 mm grid |
| T&G flooring board | 2400 × 600 mm | 18 mm, 22 mm | Floor decks and flat roofs |
| T&G flooring board, UK cover size | 2400 × 590 mm | 18 mm | Floor decks, one board per carry |
| Handy board | 1220 × 606 mm | 11 mm, 18 mm | Loft boarding, one-person jobs |
| Long handy board | 1829 × 607 mm | 11 mm, 18 mm | Loft boarding, shelving, small floors |
The sizes above are examples published by a major European OSB producer; other mills add their own lengths and widths. Plywood, for comparison, is made in 1220 × 2440 mm and 1250 × 2500 mm sheets, with custom sizes and cut-to-size panels on order. Our plywood sheet sizes guide gives the plywood side in full.
18 mm OSB board: size, weight and uses
18 mm OSB board is the heavy-duty thickness: floor decks, roof decks on wider rafter spacing, mezzanine floors and tough site work. It comes as 2440 × 1220 mm square-edged sheets, as 2400 × 590 mm T&G boards (UK cover size) and as handy boards of 1220 × 606 mm and 1829 × 607 mm.
At an example density of 600 kg/m³, an 18 mm OSB sheet of 2440 × 1220 mm weighs about 32.1 kg. The 18mm OSB T&G board of 2400 × 590 mm is half the area and lighter in proportion, which is why floor layers prefer it: one person can carry and fit a board.
Where 18 mm OSB is used, 18 mm plywood is the usual alternative. An 18 mm plywood sheet of 1220 × 2440 mm weighs 26.8 kg on a 500 kg/m³ Styrax core and 34.8 kg on a 650 kg/m³ Eucalyptus core, so the weight can go either way depending on the core. The difference that matters is the structure, covered further down.
18mm OSB board price in the UK (2026)
An 18mm OSB3 sheet of 2440 × 1220 mm costs about £18.56 ex VAT (£22.27 inc VAT) at a UK builders’ merchant in October 2026, and an 11 mm sheet about £14.00 ex VAT. The prices below are one merchant’s trade list, Selco Builders Warehouse, for SterlingOSB Zero OSB3 FSC board (a West Fraser brand) and its handy boards.
| Board | Thickness | Ex VAT | Inc VAT |
|---|---|---|---|
| SterlingOSB Zero OSB3, 2440 × 1220 mm | 18 mm | £18.56 | £22.27 |
| SterlingOSB Zero OSB3, 2440 × 1220 mm | 11 mm | £14.00 | £16.80 |
| SterlingOSB Zero OSB3, 2400 × 1200 mm | 9 mm | £14.25 | £17.10 |
| SterlingOSB Zero T&G TG4, 2400 × 590 mm | 18 mm | £14.50 | £17.40 |
| Handy board, 1829 × 607 mm | 18 mm | £22.28 | £26.74 |
| Handy board, 1220 × 606 mm | 18 mm | £14.00 | £16.80 |
| Handy board, 1220 × 606 mm | 11 mm | £8.86 | £10.63 |
Two UK details change the real cost. Handy boards and small orders usually ship on a pallet: Construction Megastore charges £85 for a pallet of up to 500 kg, with sizes and thicknesses mixed. And a merchant such as Selco gives free delivery only above £150 ex VAT, so a few sheets cost more than the shelf price suggests.
For an importer, the comparison is plywood against that shelf. An 18 mm plywood sheet of 1220 × 2440 mm holds 0.0536 m³; at our commercial plywood price from US$250/m³ (October 2026) that is a raw FOB example of about US$13.4 per sheet before freight, duty and importer margin, not a delivered price. Set the landed cost of a container of 18 mm plywood against the £18.56 ex VAT OSB shelf price, and remember that plywood holds screws near edges and takes a wet site better than OSB3.
OSB thickness chart: mm, inch and use
OSB thicknesses in Europe and the UK are metric; in North America they are fractions of an inch, a little different from the metric numbers. This chart lines them up with typical uses and sheet weights: 9 and 11 mm for walls, 12 and 15 mm for roofs, 18 mm and above for floors.
| Metric OSB | Nearest US size | Typical use | Weight, 2440 × 1220 mm at 600 kg/m³ |
|---|---|---|---|
| 9 mm | 3/8 in (9.5 mm) | Wall sheathing on timber frame, packing | 16.1 kg |
| 11 mm | 7/16 in (11.1 mm) | Walls, site hoarding, roofs on close rafters | 19.6 kg |
| 12 mm | 15/32 in (11.9 mm) | Roof decks, walls | 21.4 kg |
| 15 mm | 19/32 in (15.1 mm) | Roof decks, light floors | 26.8 kg |
| 18 mm | 23/32 in (18.3 mm) | Floor decks, heavy roofs, mezzanines | 32.1 kg |
| 22 mm | 7/8 in (22.2 mm) | Floors on wide joist spacing | 39.3 kg |
| 25 mm | 1 in (25.4 mm) | Heavy floors, platforms | 44.7 kg |
The inch sizes are converted at 25.4 mm per inch (NIST). Weights are board only, at a 600 kg/m³ example density, before packing; a real OSB sheet weighs what its own declared density gives.
OSB sheets: full sheets and T&G boards
OSB sheets come square-edged for walls and roofs, and T&G for floors where every edge must be supported. The choice decides how much framing and labour the job needs.
- Square-edged 2440 × 1220 mm: the standard OSB sheet. Edges land on studs, rafters or noggins; it is the format for wall sheathing and most roof decks.
- Square-edged 2397 × 1197 mm: slightly under the 2400 × 1200 mm grid, so sheets fit between framing set out at 1200 mm and 600 mm with a small expansion gap.
- T&G 2400 × 600 mm: a flooring board with tongue and groove on the long edges or on all four edges. The joints lock together between joists, so the long edges need no noggins.
OSB sheets swell slightly with moisture, so producers ask for a gap of a few millimetres at panel edges. Plywood moves less, but the same gap is good practice on any deck. For OSB sheets used as packing or crate panels, the square-edged 2440 × 1220 mm sheet is cut to the crate size.
OSB board 9 mm and 11 mm: which for walls and hoarding?
9 mm OSB is the common sheathing thickness for timber-frame walls; 11 mm OSB is the common thickness for site hoarding and for walls and roofs that take more knocks. Both are usually OSB/3.
9mm OSB braces the frame and carries the breather membrane and cladding fixings, while the studs carry the vertical load. It is light, about 16.1 kg a sheet at 600 kg/m³, and quick to fix.
OSB board 11mm, often called 11mm sterling board in the UK after a well-known OSB brand, is the standard for hoarding panels, because it resists impact and holds screws and paint well enough for a temporary wall. It is also the metric match for the US 7/16 in sheathing panel.
For packing and crates, both thicknesses are used, and plywood of 9 mm to 12 mm is the alternative where the crate needs a smoother face or better nail holding near the edge. Our packing plywood is made for that use.
OSB grades OSB/1 to OSB/4 under EN 300
OSB grades in Europe are set by EN 300, which defines four types by service conditions and load-bearing use. The grade matters more than the thickness when the panel is going into a building.
| Grade | EN 300 definition | Typical use |
|---|---|---|
| OSB/1 | General-purpose boards and interior fitments, dry conditions | Furniture backs, packing, display |
| OSB/2 | Load-bearing boards, dry conditions | Internal floors and walls in heated rooms |
| OSB/3 | Load-bearing boards, humid conditions | Wall sheathing, roof decks, floors, hoarding |
| OSB/4 | Heavy-duty load-bearing boards, humid conditions | Heavy floors, structural roofs |
EN 300 sits under EN 13986, the harmonised standard for wood-based panels in construction. CE marking for these panels falls under the Construction Products Regulation (EU) No 305/2011.
In the US, oriented strand board is exempt from the TSCA Title VI emission limits under 40 CFR 770.3. In practice, most 9 mm, 11 mm and 18 mm OSB sold for building in the UK and Europe is OSB/3. “Humid conditions” means a protected structure that can see damp air, not a panel left out in the rain; OSB/3 is not a waterproof board. The plywood equivalents are the EN 636 classes: EN 636-1 for dry use, EN 636-2 for humid use and EN 636-3 for exterior use.
How much does an OSB sheet weigh?
An OSB sheet weighs its density times its volume. At an example density of 600 kg/m³, a 2440 × 1220 mm sheet weighs about 1.8 kg per millimetre of thickness: 16.1 kg at 9 mm, 26.8 kg at 15 mm and 32.1 kg at 18 mm.
The same formula works for plywood, with the core species setting the density:
| 2440 × 1220 mm sheet | 9 mm | 15 mm | 18 mm |
|---|---|---|---|
| OSB at 600 kg/m³ (example) | 16.1 kg | 26.8 kg | 32.1 kg |
| Plywood, Styrax core 500 kg/m³ | 13.4 kg | 22.3 kg | 26.8 kg |
| Plywood, Acacia core 580 kg/m³ | 15.5 kg | 25.9 kg | 31.1 kg |
| Plywood, Eucalyptus core 650 kg/m³ | 17.4 kg | 29.0 kg | 34.8 kg |
An 18 mm plywood sheet on a Styrax core weighs the same as a 15 mm OSB sheet at 600 kg/m³. That matters on a container booked by weight, and on site, where sheets are lifted by hand. Our plywood density guide gives every core and thickness.
OSB vs plywood thickness tolerance
OSB is made to a wider thickness tolerance than sanded plywood. EN 300 allows ±0.8 mm on unsanded OSB and ±0.3 mm on sanded OSB, with ±3 mm on length and width.
| Panel | Thickness tolerance | Length and width |
|---|---|---|
| OSB, unsanded (EN 300) | ±0.8 mm | ±3 mm |
| OSB, sanded (EN 300) | ±0.3 mm | ±3 mm |
| Minh Thanh sanded furniture plywood | ±0.2–0.3 mm, down to ±0.2 mm | ±2 mm |
| Minh Thanh commercial and film-faced plywood | ±0.5 mm | ±2 mm |
| Minh Thanh packing plywood | ±0.5–1.0 mm | ±2 mm |
For a structural deck, ±0.8 mm is fine: the floor finish or underlayment takes up the difference. For furniture, shelving, CNC work or a thin floor finish laid straight on the deck, the tighter plywood tolerance is the reason buyers switch.
What is the plywood equivalent of OSB by thickness?
For most building uses, the plywood equivalent of an OSB board is the same thickness of structural or exterior plywood; stiffer plywood can allow a thinner deck on the same design. One published manufacturer comparison, from 2024, pairs 18 mm spruce plywood with at least 22 mm OSB for a similar floor.
| OSB board | Plywood alternative | Where plywood is the better choice |
|---|---|---|
| 9 mm OSB, wall sheathing | 9 mm exterior plywood | Walls in exposed or damp locations |
| 11 mm OSB, hoarding | 12 mm exterior plywood | Hoarding reused on several sites |
| 15 mm OSB, roof deck | 15 mm exterior plywood | Roofs left open to weather during the build |
| 18 mm OSB, floor deck | 18 mm plywood | Floors with thin finishes, wet areas, heavy point loads |
| 18 mm OSB, shelving and furniture | 18 mm furniture plywood | Any visible part, screws near edges, CNC parts |
The reasons are the build. Plywood is cross-laminated veneer, so it is stiffer for its weight, swells less at the edges when wet and holds screws closer to the edge. OSB is cost-effective where a panel only needs to brace a frame or carry a load behind a finish. Our plywood vs OSB comparison goes through the trade-off in detail.
Which panel and thickness for which part?
Choose the panel by the part’s job: bracing, decking, finishing or packing. This is the decision we walk buyers through when an enquiry starts with OSB sizes.
- Wall sheathing on a timber frame: 9 mm OSB/3, or 9 mm exterior plywood where the wall is exposed during the build.
- Site hoarding: 11 mm OSB/3, or 12 mm exterior plywood when the panels go from site to site.
- Roof decks: 15 mm or 18 mm OSB/3 by rafter spacing, or the same thickness of exterior plywood.
- Floor decks: 18 mm OSB/3 T&G on joists at up to 450 mm centres and 22 mm at 600 mm centres, as panel makers’ floor tables commonly set out, or plywood of the thickness the design calls for.
- Underlayment under vinyl, lino or thin tiles: sanded plywood, because OSB’s strand surface can show through thin finishes.
- Furniture, shelving, displays: furniture plywood; OSB/1 only where the strand look is the design.
- Crates and packing: 9 mm to 12 mm OSB or packing plywood, by the load and the exposure.
Joist and rafter spacing, loads and service class come from the building design; the panel follows them.
OSB vs plywood price: what to compare
OSB is usually cheaper per cubic metre than plywood of the same thickness, which is why it dominates wall sheathing. The fair comparison is cost per square metre of finished job, not price per sheet.
What moves the comparison:
- Thickness for the same job: if plywood allows a thinner deck, the price per square metre narrows.
- Waste and reuse: plywood hoarding and formwork can be reused; OSB edges swell after repeated wetting.
- Finish: plywood takes paint or a thin floor finish directly; OSB may need an extra layer.
- Freight: a lighter Styrax core plywood packs more sheets into a container booked by weight.
Our indicative starting prices in October 2026 are from US$250/m³ for commercial plywood and from US$350/m³ for furniture and interior plywood. OSB prices move with the North American and European housing markets, so compare a current OSB quote against a plywood quote for the same thickness, size and quantity.
How does OSB or plywood fill a 40HC container?
A 40HC of OSB fills by weight before it fills by volume at 18 mm, because the panel is dense. A 40HC of 18 mm plywood on a light Styrax core fills by volume first.
Our 40HC plan for 1220 × 2440 × 18 mm plywood, with a planning payload of 28,000 kg:
| Plywood core | Packs × sheets | Sheets | Sheet weight |
|---|---|---|---|
| Styrax, 500 kg/m³ | 18 × 55 sheets | 990 sheets | 26.8 kg |
| Acacia, 580 kg/m³ | 16 × 55 sheets | 880 sheets | 31.1 kg |
| Eucalyptus, 650 kg/m³ | 15 × 53 sheets | 795 sheets | 34.8 kg |
At 32.1 kg per sheet, an 18 mm OSB load at 600 kg/m³ reaches the 28,000 kg payload before the box is full, so OSB containers are planned by weight. For any panel, plan sheet counts from sheet weight plus packing, then cap them at the booking’s payload. The plywood weight calculator runs that plan for every plywood thickness.
What to write on the order for OSB or its plywood alternative
Write grade, thickness, size, edge and tolerance, and the use. For OSB that is a five-item line; for plywood, add core, glue and face.
OSB line:
OSB/3 to EN 300, 18 mm, 2400 × 600 mm T&G four edges, unsanded, ±0.8 mm, for floor decks.
Plywood alternative line:
Exterior plywood, 18 mm, 1220 × 2440 mm, phenolic (WBP) glue, C/D faces, hardwood core, moisture 8–12 % at dispatch, 1 × 40HC.
If you are not sure which panel the job needs, send us the use, the spacing of the joists or rafters, and the exposure. We will reply with the plywood specification we would make for it.
Where Minh Thanh Plywood fits
We make plywood, not OSB. Plywood is the alternative when a job needs a panel that is flatter, stiffer for its weight, better at the edge or more tolerant of wet weather than OSB.
The plywood lines that replace OSB in those jobs:
- Exterior / CDX-type plywood: low-grade C/D faces with water-resistant melamine-fortified or phenolic (WBP) glue, for wall sheathing, stair treads and outdoor uses.
- Commercial and packing plywood: cost-effective panels for crates, pallets and hidden parts, at ±0.5 mm and ±0.5–1.0 mm.
- Film-faced plywood: phenolic film faces for concrete formwork and reusable hoarding.
- Furniture plywood: for shelving, displays and anything visible, sanded to ±0.2 mm.
All are made in 1220 × 2440 mm and 1250 × 2500 mm, in 3–40 mm, with MOQ one 40HC and mixed specifications by agreement, and certificates and test documents for each order; production takes 15–45 days after the 30% deposit. Send the OSB size and use you are replacing through the exterior plywood page, and ask for free samples to compare side by side.
Buyer questions, answered
What size is an 18 mm OSB board?
A full 18 mm OSB board is usually 2440 × 1220 mm (8 × 4 ft) or 2397 × 1197 mm. For floors, 18 mm OSB is also made as tongue-and-groove boards of 2400 × 600 mm.
How much does an 18 mm OSB sheet weigh?
At an example density of 600 kg/m³, an 18 mm OSB sheet of 2440 × 1220 mm weighs about 32.1 kg. Use the density on the producer's declaration for a real order.
What is 7/16 OSB in mm?
7/16 inch OSB is 11.1 mm, sold in Europe and the UK as 11 mm OSB. It is the common wall sheathing and hoarding thickness.
What is 11 mm sterling board?
Sterling board is a UK trade name for OSB. 11 mm sterling board is an 11 mm OSB sheet, usually OSB/3, used for wall sheathing, site hoarding and roof decks on close rafters.
Is 9 mm OSB strong enough for walls?
9 mm OSB is a common sheathing thickness for timber-frame walls, where the studs carry the load and the board braces the frame. For hoarding or walls that take impacts, 11 mm or more is usual.
What is the standard OSB sheet size?
The standard OSB sheet size is 2440 × 1220 mm (8 × 4 ft). Some producers also make 2397 × 1197 mm sheets and 2400 × 600 mm T&G flooring boards.
Which OSB grade should I buy?
For most building work in the UK and Europe, buy OSB/3, the load-bearing grade for humid conditions under EN 300. OSB/2 is for dry conditions; OSB/4 is the heavy-duty humid-use grade.
What is the plywood equivalent of 18 mm OSB?
For floor and roof decks, 18 mm plywood is the usual like-for-like swap for 18 mm OSB, and stiffer plywood can allow a thinner deck on the same design. One published comparison pairs 18 mm spruce plywood with at least 22 mm OSB.
What is the OSB thickness tolerance?
EN 300 allows ±0.8 mm on unsanded OSB and ±0.3 mm on sanded OSB, with ±3 mm on length and width. Our sanded furniture plywood is made to ±0.2–0.3 mm and ±2 mm on length and width.
Is 18 mm OSB or plywood better for underlayment?
For underlayment under finished floors, sanded plywood is flatter and has no strand pattern to telegraph through thin vinyl or lino. OSB at 18 mm is common as a structural deck, with a separate underlayment on top.