OSB Thickness and Board Sizes Guide

Building cabins, sheds, garages, houses, and even shelving can be an expensive process today. To help reduce costs, many are using OSB (oriented strand board) instead of other, more costly materials. Like plywood, OSB thickness and density determine its strength and how it can be used.

OSB is manufactured with squared edges with 19/32” or greater in thickness also available with tongue and groove finishes on their long sides. Produced in dozens of imperial and metric thicknesses from 15/64 or 6mm to 1-1/2” or 40mm and dimensions of 4×8, 4×9, 4×10, or comparable metric sizes. OSB can be used for a multitude of purposes, including floors, walls, ceilings, roofs, and shelving.

In this guide, we’ll explain the difference between the actual and nominal thicknesses of OSB and provide a reference Chart comparing the thickness. We’ll also discuss common thicknesses used for different applications and identify typical OSB sheet sizes and dimensions. Our aim is to provide you with a complete guide to assist you in the selection of materials for your next project.

OSB Thickness

Actual vs Nominal Oriented Strand Board Thickness

The actual thickness of most solid or manufactured wood products varies from its nominal thickness. A nominal 2×4 is actually 1-1/2” by 3-1/2” and the actual thickness of a sheet of OSB or plywood is usually 1/32” less than its nominal dimension. However, moisture content and other factors can cause those thicknesses to fluctuate.

OSB is available in nominal thicknesses from 15/64” or 6mm to 1-1/2” or 38mm. But even those nominal thicknesses aren’t always accurate but often rounded; the 1-1/2” is really 1.565 or 40mm.

OSB, like most plywood, is manufactured to a specific or nominal thickness, and then sanded on one or both sides. Sanding typically takes 1/32” or about 0.8mm off the thickness, so nominal and actual thickness will differ by about 1/32 of an inch or almost 1mm.

Unfortunately, milling machines and glues and the calibration of presses and temperature controls from one mill to another can also affect thicknesses. The nominal thickness may be identified, but the actual, although sometimes stamped on the sheet, may also vary. Caliper measurements of OSB sheets from different mills and even within the same bundle from one mill can vary significantly.

A recent wander through three local national home improvement box stores measuring OSB thickness was eye-opening. The thickness of 1/2″ OSB ranged from 0.459” to 0.516” and 3/4″ OSB from 0.710” to 0.766”. That means the actual thickness can fluctuate almost 1/16” from sheet to sheet.

Sanding may account for the loss of 1/32”, which is 0.0313 of an inch, but the rest is due to other factors. So, if the actual thickness is important, take calipers to the lumber yard and only select panels of similar thicknesses.

OSB Thickness Chart

OSB Thickness

OSB is available in nominal thicknesses from 15/64 (6mm) to 1-1/2” (40mm). The nominal thicknesses are fairly standard, but the actual thicknesses tend to vary. On average, the actual thickness is approximately 1/32” or 0.8mm less than the nominal thickness. However, the nominal thickness isn’t necessarily accurate either – 3/8” converts to 9.525mm or 9.5mm, but is often given the nominal thickness of 9mm.

Many mills have begun to print the ‘actual’ thickness on OSB boards instead of the nominal thickness for some common dimensions. For example, some nominal 1/2” thick panels are being stamped 15/32” and 3/4” sheets 23/32”. However, there are also nominal 15/32” and 23/32” thick panels.

This may cause some confusion. Plus, metric panels produced for the North American (N.A.) market tend to be a converted thickness comparable to the Imperial equivalent.

Products to or from the global market tend to be manufactured truer to the SI or metric system. So, while 3/8” would be 9.5mm, but may be identified in North America as 9mm, a true nominal 9mm panel would be thinner than a comparable 3/8” one.

The most readily available or common thicknesses tend to be those frequently used for construction. The Table below identifies the nominal and actual thicknesses commonly available in N.A for OSB panels.

Common North American OSB Thickness Chart
Nominal Thickness Actual Thickness*








3/8” 9.5mm 177/500” or 0.354” 8.99mm
7/16” 11mm 13/32” 10.319mm
15/32” 12mm 29/64” 11.509mm
1/2” 12.7mm 15/32” 11.9mm
19/32” 15mm 37/64” 14.684mm
23/32” 18mm 45/64” 17.859mm
3/4” 20mm 23/32” 18.256mm
7/8” 22mm 27/32” 21.431mm
1-1/8” 28.5mm 1-3/32” 27.781mm

* The ‘actual’ thickness may vary from panel to panel.

Common OSB Thickness for Different Applications

OSB thickness for roof

OSB, like plywood, is used for a variety of structural and non-structural purposes in different building industries. The thickness of the material, along with other factors, affects its strength, and thus where and how it can be used.

The nominal thickness is generally the determining factor when selecting OSB for a project. The stamp on the back of OSB panels identifies its grade, exposure rating or binder type, thickness, span rating, orientation to supports or strength axis, edge spacing, and which side should be down or inward, plus other information.

The stamp also includes end-use marks such as 1F, 2F, 1R, 2R, and W. The ‘1’ identifies that it doesn’t require edge support and the ‘2’ means it requires blocking or H-clips for edge support. The letter identifies use or application, with F-floor, R-roof, or W-wall.

The span mark commonly identifies the distance between supports for that sheet thickness as 16”, 20”, 24”, 32”, 40”, or 48”. Spans less than the identified spacing are acceptable too.

Different thicknesses are commonly used for specific purposes. Below, we identify common thicknesses used for different applications.

Roof Decking

Roof Decking

The thickness of OSB used for roof decking depends on the truss or rafter spacing and span, plus the type and weight of the roof finish, pitch, snow load, and other factors. The minimum thickness of OSB is usually 5/8” or 15mm, although 3/8” is acceptable for light loads.

Many professionals, though, prefer to use 3/4″ or 20mm T&G (tongue and groove) OSB for 16” or 24” support spacing. The thicker panel is stronger and rated for 175psf of live load, and coupled with the T&G edge won’t sag over time.

The stamp on the OSB should identify it as ‘Exterior Bond” or something similar, which means a waterproof adhesive was used in its manufacture.


Interior wall sheathing can range from 1/4” to 1-1/2” depending on the purpose of the space it is enclosing and local code requirements. OSB adds strength to walls and can be covered with drywall or other materials. It helps reduce thermal conduction and sound transfer and can be left exposed and painted, stained, or clear-coated as a design feature. Sheathing used for damp or moist locations is usually ‘Exterior Bond’ grade.


The thickness of OSB for floors depends on joist spacing and the weight of the flooring it will need to support. For joists spaced at 16” centers, the minimum thickness is commonly 23/32” and for joists at 24” centers 1”, but always check with your local building department.

Many contractors use 3/4″ or 7/8” OSB for joists spaced at 16” centers for added strength. Edges should be blocked or T&G to prevent flexing or sag. It is also recommended that an underlayment be used over OSB as some flooring adhesives have difficulty bonding to it.

Exterior Walls

OSB Interior wall sheathing

The thickness of OSB used for exterior walls is typically 3/8” (9.5mm) or 7/16” (11mm). The US Department of Energy identifies 7/16” as the minimum for exterior walls and 3/8” for enclosing gables. Most building codes recommend stucco be applied to sheathing at least 1/2″ thick.

Regions prone to wind extremes also tend to require thicker wall material. Many builders commonly use 1/2″ or 5/8” as their standard wall sheathing. Exterior wall sheathing should be identified as ‘Exterior Bond”, while interior use need not be.

Attic Floor

The attic floor thickness depends on the spacing of the ceiling joists that form the attic floor and the anticipated loads the floor will support. Plus, the size of the attic, joist span, and local code requirements.

Ceiling joists spaced at 16” centers and rated for 5 to 10psf are okay for light storage or infrequent use, so 7/16” or 1/2″ OSB is often used. It’s common, though, to use 5/8” or 23/32” or thicker OSB for joist spacing 16” or 19.2” apart respectively, 7/8” if spaced 24” apart, and 1-1/8” if 32” apart.

Always check with the local building department and ensure the attic floor is designed to support the weight required.

Shed Roof and Floor

The OSB recommended for shed floors and roofs usually depends on floor joist and rafter spacing and span, and on the loads each will need to carry. It is common to use 23/32” or 3/4″ T&G OSB for shed floors with joists spaced up to 16” O.C. and 7/8” or 1” is recommended if roof supports are spaced at 24” centers.

The roof material also depends on rafter or truss spacing, span, slope, and exterior finish, plus the shape and type of roof and any local code requirements. It may be acceptable to use 7/16” for rafters spaced 16” apart, but 5/8” is more commonly used as it won’t sag. For rafters spaced at 24” centers, 23/32” or 3/4″ OSB is frequently used.

Garage Walls

Exterior garage walls, like house walls, are usually sheathed in exterior rated 1/2″ or 5/8” OSB. It may be within code specs to use 3/8” or 7/16”, which could help the budget, but may increase other costs. Some local codes require a 5/8” minimum, which provides a better thermal barrier and offers greater sound control.

Many homeowners also use 3/8” to 1/2″ OSB to finish the inside walls of the garage. It paints up well, is more impact resistant than drywall, and is better for holding nails or screws supporting tools and whatnot.


The depth and length of shelving and the spacing of supports, plus the potential loads will impact the thickness of OSB required for shelving. Shelves that are only 12” deep usually need lateral support every two to three feet if 3/8” OSB is used.

For 24” wide shelves use 3/4″ OSB with cross brace supports every 24” to 48” in length depending on loads to prevent sag. If using OSB to build verticals and horizontals, the nail-holding ability of 3/4” OSB is better than that of 5/8”.

Common OSB Sheet Sizes and Dimensions


OSB is available in nominal Imperial sizes of 4’x8’, 4’x9’, and 4’x10’ panels, as well as fractional sheet sizes of 2’x8’, 4’x4’, 2’x4’, and 2’x2’, plus their metric equivalents. The length and width measures are actually 1/8” smaller than their nominal measure, so 4×8 panels are actually 47-7/8”x95-7/8”. OSB is available in other lengths and widths depending on location, and can even be ordered in 8’x24’ or longer panels.

The thicknesses of OSB available at any location often depend on the local market needs, but other dimensions can usually be ordered. The most commonly carried by retailers is 3/8”, 1/2″, 5/8”, and 3/4″ thicknesses, but 7/16”, 15/32”, and 23/32” are often available with or instead of 1/2″ or 3/4″ measures.

The most common thicknesses are those typically used in the construction industry. Other sizes may make regular or irregular appearances at your local supply store depending on availability. However, if you buy irregular thicknesses, purchase extra for your project as it may be difficult to find later.

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