When we use the term plywood today, it is a general term, referring to a whole family of engineered wood products, all of which are produced in panels. While there are a variety of different products that fall into this definition, not all of them fit the description of traditional plywood. However, each of them fulfills a specific purpose for which they have been designed.
Different types of plywood are produced in a range of thicknesses from 1/8” to 1-1/4” thick. However, not all types of plywood are available in all of the various thicknesses that are being manufactured. A lot depends on what the specific plywood product has been designed to be used for. This chart gives you an idea of the standard thicknesses of the most common types of plywood:
| Plywood Thickness: | 1/8″ | 1/4″ | 5/16″ | 3/8″ | 7/16″ | 1/2″ | 5/8″ | 3/4″ | 1-1/8″ | 1-1/4″ |
|---|---|---|---|---|---|---|---|---|---|---|
| Softwood Plywood |  | | | | | | ||||
| Hardwood Plywood | | | | | ||||||
| Luan Plywood | | | | | ||||||
| Marine Plywood | | | | | | | | |||
| Particle Board | | | | |||||||
| MDF | | | | | | | | | ||
| MDO | | | | | ||||||
| OSB * | | | | | | | | |||
| ApplePly * | | | | | | | |
|||
| Baltic Birch ** | | | | | | |
Notes for this chart:
* Also available in additional thicknesses.
** Please note that Baltic Birch is produced to metric dimensions. The dimensions here are approximate equivalents.
While 3/4” thick plywood is the thickest that is sold in sheets in most lumberyards and home improvement centers, plywood is commonly manufactured in 1” and 1 ¼” thick sizes as well. Some mills produce plywood up to 3” thick for special order. These thicker plywood products are typically used in specialized furniture making, such as tops for industrial workbenches.
Sheets
Most plywood products are commonly available in standard 4’ x 8’ sheets, regardless of thickness. Baltic Birch is more commonly available in 5’ x 5’ sheets, which is the standard European size for plywood. Even so, manufacturers of Baltic Birch, like those of other plywood products currently manufactured in Europe, are gradually switching over to the American standard of 4’x 8’ sheets.
But Baltic Birch is not the only plywood product manufactured in 5’ x 5’ sheets; many hardwood plywood products are also produced in this size, especially when manufactured in Europe, for the European market. Although the 4’ x 8’ sheet size is the most common, some types of plywood are also produced in 4’ x 10’ and 4’ x 12’ sheets for industrial applications. For example, OSB is manufactured in sheets up to 24’ long. The largest sheets of any type plywood that would be available is 6000mm x 2200mm (19’-8-1/4” x 7’-2-5/8”). However, any of these larger sizes would normally only be available by special order.
Generally speaking, a 4’x 8’ sheet of plywood will measure exactly 48” wide and 96” long. It is rare to find it off by more than 1/32” or so. Mills cut the plywood to exacting dimensions, because it is necessary in the construction of homes and other buildings. If sheets were only 1/8” long or wide, subflooring would be off the edge of floor joists, wall studs or rafters in six sheets. The only way to prevent that would be for carpenters to finish cutting every panel, before installing it, an expensive undertaking.
Some retailers also offer project panels, especially for hardwood plywood, which are smaller than full sheets. While 2’x 4’, 2’x 2’ and 4’x 4’ are the most common sizes for these, a variety of other sizes are available, such as 10”x 30”. These retailers are trying to meet the needs of their customer base, marketing panels which are a fit for common project plans.
Nominal and actual thickness
There are two different thickness definitions we need to keep in mind when talking about plywood; that of nominal thickness and actual thickness. Just like dimensional lumber, most plywood is rated at a nominal thickness; the thickness before it is sanded. The actual thickness is just like it sounds – the actual thickness of the plywood panels you buy, after sanding. Typically, the actual thickness of plywood is 1/32 inch less than the nominal thickness.
Part of the reason for this difference is industrial manufacturing, where plywood is used in product design. Industrial machinery which handles and machines plywood for furniture and cabinetry can handle material that is slightly thinner, without problem. But when that material is thicker than nominal, it is a problem for those operations, especially joining parts together.
Rather than concerning ourselves that the plywood is too thin, we should remember that dimensional lumber is considerably smaller than it’s nominal dimension. By comparison a 1”x 4” board is 3/4” x 3-1/2”, a full 1/4” thinner and 1/2” narrower than the nominal dimension. That makes the 1/32” of difference in the nominal and actual thickness of plywood seem much more trivial.
The table represents the comparison between nominal and actual softwood plywood thickness:
| Nominal Thickness | Actual Thickness |
|---|---|
| 1/4” | 1/4” |
| 3/8” | 11/32” |
| 1/2” | 15/32” |
| 5/8” | 19/32” |
| 3/4” | 23/32” |
| 1-1/8” | 1-1/8” |
Most lumberyards have switched over to listing the plywood on their racks in the actual thickness, rather than the nominal thickness. That’s nice from the viewpoint of honesty, but it can be a head scratcher when you’re standing there looking at it and trying to decide what you need to buy.
The trick here is understanding what a half inch is in that actual thickness. Since they are listing it in 32nds of an inch, we need something that is about half of that, or 16/32. What we have is 15/32”. If you can remember that one thickness, you’ve got it made. To get 3/4”, all you do is add a half of 15 to the 15 that’s above the line, which means you want something that’s about 22/32”. As you see in the chart above, we’ve got 23/32”; so that has to be the 3/4” equivalent. The other thicknesses fit between these two, making it easy to see what they are.
Please note that even the “actual thickness” isn’t a perfect dimension, but an approximation. If you were to measure that sheet with a pair of dial calipers (or digital calipers), you would find that it isn’t exactly that thickness. Rather, it will vary slightly, due to the manufacturing process.
This variation is fairly consistent in any bunk of plywood, as the whole bunk comes from the same mill and is made at the same time. What makes the variation exist isn’t the laminating process, but rather the sanding process. Settings on the machine and wear on the sanding belt can easily cause those slight variations. To prevent them causing a problem on a project, it is best to buy all the plywood for the project at the same place and the same time.
Moisture can affect the thickness of plywood products as well. When the plywood is manufactured, there is a certain amount of water in the wood veneers. As that sheet dries further, the plywood will become slightly thinner. Should the sheet be left in a high moisture environment, it will gradually become slightly thicker again.
This change in the thickness of the plywood can work to pull nails loose; not all the way loose, but enough to be noticeable. The use of screws or adhesive to hold plywood parts together on a project will eliminate the risk of the fasteners loosening up from cycles of absorbing moisture and drying.
Thickness in millimeters
Although measures in inches are the most common, some thicknesses are expressed in millimeters, especially for plywood products manufactured in Europe. Probably the best example is Baltic Birch plywood (sometimes called Russian or Finland Birch). Another plywood product which is typically sold in metric thicknesses is aircraft plywood, a product which was common during World War II, but not so common today.
| Thickness (inch) | Thickness (milimeter) |
|---|---|
| 1/8” | 3.2mm |
| 1/4” | 6.4mm |
| 5/16” | 8mm |
| 3/8” | 9.5mm |
| 7/16” | 11.1mm |
| 1/2” | 12.7mm |
| 5/8” | 15.9mm |
| 3/4” | 19mm |
| 1-1/8” | 28.6mm |
| 1-1/4” | 31.75mm |
When making your selection, you want to avoid misunderstanding what the actual thickness is of any plywood product you buy. You can best avoid those misunderstandings, by taking the time to look at and understand dimension comparison between these two units of measure. Also, be careful and keep it in mind when comparing the prices.
Selecting plywood thickness
In many cases, the selection of a particular thickness of plywood is based more upon the convenience of using that thickness of plywood for the work being done, than anything else. Plywood is strong enough, that it usually provides more strength and stiffness than is needed in a particular application.
Nevertheless, there are applications where the strength and stiffness of the plywood is the determining factor in selecting a particular thickness of plywood. Such is the case for plywood structural elements used in the construction of homes. The same can apply to a wide range of other applications, such as making some types of furniture and shipping crates.
There are several factors, associated with the thickness of the plywood and how it is installed, which affect the strength and stiffness of a particular type of plywood sheet:
- Thickness – obviously, the thicker the plywood sheet, the stronger and stiffer it is
- Number of Plys – the more individual layers the sheet of plywood has, the stronger and stiffer it is
- Support Span – the farther apart that supporting elements are spaced, the more of a chance for the plywood to flex
- Direction – plywood is stronger along the “strength axis,” which is the axis parallel to the face veneer. That is because it has one more ply with the grain running in that direction
The most obvious of these factors is the thickness of the plywood. Just how strong is a bit hard to understand. While the various types of plywood have been tested over the gambit of support options that might be encountered, the resulting data is not presented in a manner the layperson might understand. Part of this is because of the wide variety of support options used in construction and how much that support affects the strength of any structure built out of plywood.
Nevertheless, we can gain some insight into the strength of different thicknesses of plywood by looking at the requirements in the building code. Floors, which are designed to support a minimum of 50 pounds per square foot, are built out of 3/4” thick softwood plywood or OSB. While that 50 lbs. may not seem like much, we have to take into account that it is over floor joists that can be as much as 24 inches apart. So we’re talking 100 pounds between any two floor joists. At that span, the problem is flexion, more than anything else. While the plywood could support more, you’d probably feel uncomfortable walking on it.
Roofs, which can be sheathed with 3/8” thick softwood plywood, in most jurisdictions, are designed to carry a load of 20 pounds per square foot. Once again, the rafters are allowed to be 24” apart. To put that in perspective, 10 inches of fresh snow weighs about five pounds per square foot. So a roof made out of 3/8” softwood plywood, over 2”x 6” rafters spaced every 24” can support 40 inches of snow.
Please note that this is “fresh fallen snow.” Snow tends to pack down as it accumulates; so if you have snowstorms sufficiently close together that the snow from one hasn’t melted before the next snowfall, the overall weight will be more than 5 lbs. per square foot for the total accumulation. For that reason, areas of the country with high snow accumulations may require that roof sheathing be 1/2” softwood plywood, as a safety precaution, increasing the dead snow load up to 30 lbs. per square foot.
Plywood for construction
Softwood plywood is commonly used in the construction of homes and other buildings. Since homes are typically wood framed, there is a considerable amount of plywood in the average home. This plywood is used for roof sheathing, walls sheathing and subflooring. The thicknesses of plywood most often found used in home construction are 3/8”, 1/2” and 3/4”.
Actual thicknesses and plywood products used in the construction of a home depend on the building code used in that municipality. While most cities use the Uniform Building Code (UBC) or the International Building Code (IBC), some cities have adopted state or local building codes. Of these two standards, the UBC is older and has to a large part been replaced by the IBC.
While it’s easy to say that local building codes are nothing more than bureaucracy run wild, the truth is that some jurisdictions have determined that the requirements in the UBC or IBC are inadequate to their residents’ needs, usually due to weather considerations. Roof load requirements for a home built in Alaska, where they get much more snow, are a much bigger issue than they are for Florida. Therefore, the building code in Alaska may be modified, requiring thicker sheathing and stronger rafters.
Leaving that aside for the moment, the following standard thicknesses can be expected. However, you should be sure to check on requirements where you live, before starting any construction project, just to ensure that your project will pass inspection.
- Roof sheathing – 3/8” or 1/2” CDX softwood plywood
- Wall sheathing – ½” CDX softwood plywood. However, this is only required in the corners of the building. The rest of the sheathing can be Styrofoam insulation
- Subflooring – 3/4” softwood plywood or OSB
7/8” plywood subflooring
As construction techniques have changed over time, so have the materials being used for the construction of homes. One such change is the increase of spacing for floor joists from 16” centers to 24” centers. While this meets the technical requirements of the IBC, it produces a floor which is more susceptible to flexing, creating squeaks and a “spongy” feeling when walking on it.
This can be even more of a problem for homes built with ceramic tile or wood flooring. These types of flooring need a solid subfloor, which will not flex. Flexing of the subfloor under ceramic tile can cause the mastic to come loose of the tile, the grout to break out from between tiles and the tiles themselves to break. In such cases, the solution is to upgrade the 3/4” nominal subfloor to 7/8” subflooring (actual dimension). The thicker 7/8” subfloor provides double the stiffness of 23/32” OSB subflooring.
This is a more cost effective solution than putting in a double layer of 3/4” plywood subflooring, something that is done during remodeling projects where ceramic tile floors are to be installed over wood subfloors that are only 3/4” thick.