If you are a DIY enthusiast working on woodworking projects, you must have come across plywood sheets of different thicknesses.
But did you know that their actual thickness varies from their nominal thickness?
- A ¼" (0.25") sheet actually has a thickness of ⁷⁄₃₂" (0.22")
- A ½" (0.5") sheet actually has a thickness of ¹⁵⁄₃₂" (0.468")
- A ¾" (0.75") sheet actually has a thickness of ²³⁄₃₂" (0.718")
How thick is plywood?
Plywood sheets are available in various thicknesses ranging from 1/8" to 1-1/4", with 3/8" to 3/4" being the most commonly available thicknesses. These plywood sheets are available in grades, with A-grade being the best quality plywood and D-grade being the lowest quality option.
This article will provide a detailed guide on plywood thickness and present a chart to help you select the right plywood according to its available thickness.
Nominal and Actual Plywood Thickness
|⅛" (0.125")||3 mm||³⁄₃₂" (0.09")||2.28 mm|
|¼" (0.25")||6 mm||⁷⁄₃₂" (0.22")||6 mm|
|⁵⁄₁₆" (0.3125")||8 mm||⁹⁄₃₂" (0.28")||7.11 mm|
|⅜" (0.375")||10 mm||¹¹⁄₃₂" (0.343")||9 mm|
|⁷⁄₁₆" (0.438")||11 mm||¹³⁄₃₂" (0.406")||10.3 mm|
|½" (0.5")||13 mm||¹⁵⁄₃₂" (0.468")||12 mm|
|⅝" (0.625")||16 mm||¹⁹⁄₃₂" (0.593")||15 mm|
|¾" (0.75")||19 mm||²³⁄₃₂" (0.718")||18 mm|
|1⅛" (1.13")||28 mm||1⅛" (1.13")||28 mm|
When looking for the right plywood for your project, you should remember that plywood has two types of thickness: nominal thickness and actual thickness.
Nominal thickness is the standard thickness that is generally mentioned in the description of the plywood.
However, the actual thickness of the board can be less than the nominal thickness by around 1/32".
This is primarily because of the sanding operation performed on the sheets after manufacturing them.
Apart from that, the actual thickness of the plywood can also vary due to the moisture content present in the veneers at the time of manufacturing, which leads to thinning of the board after drying.
So how can you ensure uniform thickness for your project?
The best way to ensure uniform thickness in your project is to buy the plywood manufactured in the same lot.
This ensures similar moisture content with similar sanding operations, leading to a uniform thickness of the plywood sheets.
Plywood Thickness Chart
Plywood sheets are generally available in variable thickness options ranging from 1/8" (0.125") to 1-1/8" (1.13").
However, the most commonly available sizes are 1/4", 3/8", 1/2", 5/8", and 3/4".
The table above presents the standard thickness of boards that are readily available on the market. However, these boards can also be available in other thickness options, depending on the manufacturer.
Softwood plywood consists of veneers of softwoods, such as cedar, pine, Douglas fir, etc.
These plywood are used for applications where good load capacity is desirable, irrespective of the surface finish.
Generally, these plywood are available in thicknesses ranging between 1/8" to 1-1/4".
However, the general-purpose softwood plywood used for home improvement and DIY projects is a 3/4" thick 5-ply board.
It is suitable for projects such as general-purpose shelves, attic flooring, roof and wall sheathing, laser cutting, etc.
Despite its good strength, softwood ply is not suitable for outdoor applications as it is susceptible to quick wear under environmental conditions.
Hardwood plywood is made of wood such as oak, maple, cherry, walnut, birch, etc.
It is suitable for projects where a high surface finish is required along with good load capacity.
Generally, hardwood boards are available in 1/4", 3/8", 1/2", and 3/4" thickness options.
While 3-ply boards hardwood boards are suitable for indoor applications, 5-ply is suitable for outdoor applications, whereas, 3/4" 7-ply boards are recommended for heavy-duty load-bearing applications like framing and roofing.
Marine Grade Board
Marine grade boards are made from hardwood such as Douglas fir or pine.
Unlike standard hardwood boards, these boards consist of thin veneers without the presence of knots.
This prevents voids in the structure, thereby minimizing the risk of moisture seeping into the board and providing excellent fastener-holding capability.
Apart from that, the veneers of marine grade plywood are glued together by a water-resistant adhesive, that helps them retain their structural integrity, even when subjected to marine applications.
Generally, marine-grade plywood is available in 1/2" and 3/4" thickness with some manufacturers producing 3/8" and 5/8" thick boards as well.
Due to their excellent wear resistance, even when subjected to water, these boards are used for outdoor applications and making boats.
It must be noted that, despite having water resistant adhesive, these boards are not immune to moisture or rot, and require a coating of paint or varnish to enhance their water resistance.
Unlike other plywood, particle boards consist of wooden particles glued and pressed together to form a high-density board.
These boards are lightweight and suitable for making furniture, cupboards, work tables, and other low-load projects.
When compared to standard plywood, particle board cannot handle high loads and is therefore not suitable for construction applications.
Depending upon the manufacturer, particle boards are available in various sizes.
However, it is advised to use particle boards having thicknesses greater than 3/4" for household applications that require good load-bearing capabilities.
Luan plywood, also known as lauan plywood, is a special type of hardwood plywood made from tropical hardwood.
These plywoods are available with 1/8" and 1/4" thickness options and are best suited for applications such as flooring underlayment, shelves, and other DIY projects.
Despite their good strength capabilities, luan plywood is generally more lightweight than regular hardwood plywood.
Baltic Birch Plywood
Baltic birch plywood is a special type of plywood with around 0.04" (1mm) thick birch veneers in its core.
These solid veneers are bonded together with a strong adhesive, eliminating any voids in its core.
As a result, baltic birch plywood is strong, durable, and steady throughout its length.
Baltic birch plywood is generally available in an odd size of 5' x 5' with thicknesses varying from 1/8" to 3/4".
Its excellent surface finish and good load-bearing capacity make it ideal for various types of projects ranging from furniture to making work beds for CNC routers.
Apart from that, it is also suitable for laser cutting applications and producing an excellent contrast when laser engraved.
MDF or medium-density fiberboard is not a type of plywood but is readily used as an alternative to plywood in various applications.
It is an engineered board made from fine fibers of wood bonded together by a resin and pressed into panels.
These boards are similar to particle boards but provide comparatively better durability.
MFD boards are best suited for indoor applications like cabinetry, cupboards, desks, etc., and are not suitable for outdoor applications due to their poor water resistance.
These boards are available in variable thicknesses ranging from 1/8" to 1-1/8", and selecting the right thickness for your project will help you achieve the best results.
Generally, MDF boards require a coating of sealant such as varnish to enhance its surface finish, presenting a dark shade similar to walnut.
MDO or medium-density overlay is a special type of plywood that is made from wood fibers bonded together with a waterproof resin.
Unlike MDF, it is highly resistant to water and is best suited for outdoor applications.
Although it is much more expensive than other types of plywood, it provides an excellent weight-to-strength ratio and long life, suitable for outdoor applications in construction.
Generally, it is available in various sizes ranging from 3/4" to 1", making it suitable for a variety of indoor and outdoor projects like making sign boards on a CNC router, cabinetry, floor, and wall panels, etc.
OSB or oriented strand board is a type of engineered panel that is made up of small rectangular strands of wood placed in a cross-orientation and bonded together with a heat-cured, waterproof resin.
However, these boards are not completely waterproof and require protective coatings such as paint or varnish to enhance their resistance to moisture.
OSB provides a low-cost alternative to plywood for sheathing applications for floors, walls, ceilings, etc.
Apart from that, OSB is also used for making table tops, furniture, and other indoor projects.
Generally, OSB is available in a wide range of thickness options from 1/4" to 1-1/8".
Selecting the Right Plywood Thickness
|Application||Recommended Plywood Thickness|
|Walls Sheathing||3/8" to 1/2"|
|Roof Sheathing||1/2" to 5/8"|
|Sub-Flooring||5/8" or 23/32" for OSB|
|CNC Cutting||According to the machining capability of your router|
|Laser Cutting||3/16" for 20W diode laser|
The optimal plywood thickness mainly depends upon the dimensional requirements of the project and the type of application.
Generally, the thickness requirement of the plywood depends upon the number of plies, the strength axis, and the available support to the plywood.
1/4" thick plywood can be available in 3-ply and 5-ply options. Although both provide the same thickness, the plywood with more plies provides greater strength and rigidity.
Furthermore, aligning the strength axis of the plywood with the direction of load ensures high load-bearing capability with minimal thickness.
The strength axis of the plywood runs parallel to the direction of the grains of the face and back veneers of the plywood. A plywood sheet is the strongest along this axis.
Apart from that, the distance between the supports also plays an important role in determining the optimal plywood thickness.
This can be understood from the example that, when using a 3/4" thick plywood, with support elements separated by a distance of 24", the plywood sheet can easily take up a load of a grown man's weight.
Increasing the distance between the supports will lead to buckling of the plywood and eventually cracking under the action of the load.
However, if the application demands prolonged distance between the supports, it is advised to use thicker plywood with more number of plies to provide greater strength.
When cutting plywood on a CNC router or a laser cutter, the specification of your machine determines the optimal thickness of the plywood.
Therefore, it is important to identify your requirements and select the appropriate plywood thickness for your application.
Plywood sheets are available in various thickness options, and selecting the right thickness for your application will ensure the sturdiness and long life of your project.
Generally, the thicker the plywood, the greater its strength and rigidity, but increasing the number of plies and reducing the distance between supports also enhances the strength of the plywood.
Therefore, for an application with dimensional constraints, using plywood with more plies will ensure the required strength without affecting the thickness of the board.
If a project requires you to cut down the thickness of plywood, you can do so by planing plywood using a powered or manual planer.
But it may expose the plywood core and weaken its structure, so it's always best to find plywood having a thickness close to your requirement.
Frequently Asked Questions (FAQ)
What is the standard size of plywood sheets?
The standard size of plywood sheets is 4' x 8' which covers a rectangular area of 32 sq. ft. However, plywood such as baltic birch plywood is available in the standard size of 5' x 5', which covers a square area of 25 sq. ft.
What are the grades of plywood?
The grades of plywood are A, B, C, and D. While A-grade plywood is the best quality plywood with no voids or knots in the veneers and has a smooth surface finish, B-grade plywood can have a comparatively rough surface, C-grade plywood can have knots up to 1.5" in diameter, whereas D-grade plywood has the lowest quality with voids in the veneers and the knots can be as big as 2.5" in diameter.
What is the thickest plywood available on the market?
The thickest plywood size generally available for most types of plywood is 3/4". However, depending on the type of plywood and the manufacturer, you can also find plywood sheets as thick as 1-1/4".