Plywood is used for subfloors, stairs, sheathing, shelving, cabinetry, furniture, toys, and literally thousands of other uses. It’s an engineered wood panel building material and a DIYer staple. If you’ve ever wondered how much weight can plywood hold, we’re here to help.
The number, thickness, and density of the wood layers that make up plywood affect how much it can hold, as do its span and other factors. Typically, softwood plywood 1/4” thick can hold 5psf, 1/2″ 35psf, 3/4″ around 80psf, and 1” approximately 164psf. Panels of the same thickness with more plies are stronger, as are those made of hardwood layers.
In this article, we’ll identify how much weight plywood can hold, factors affecting plywood’s strength, its bending strength, and the strongest plywood. We’ll compare its strength to wood, MDF, and OSB, and explain how to make plywood stronger. We even explain how a plywood load capacity calculator works, and provide a link to one. Our goal is to provide you with the information you need for your plywood projects.
- How Much Weight Can Plywood Hold?
- What Does Affect Plywood Strength?
- Plywood Strength Chart
- Plywood Load Capacity Calculator
- Plywood Bending Strength
- Is Plywood Stronger Than Wood?
- Is Plywood Stronger Than MDF?
- How to Make Plywood Stronger?
- Is Plywood Stronger Than OSB?
- What Is the Strongest Plywood?
How Much Weight Can Plywood Hold?
Typically, the greater the unsupported distance and thinner the plywood, the less it can support. A 1/4” sheet of softwood plywood can support about 5psf (pounds per square foot), 1/2″ can carry about 35psf, 3/4″ around 80psf, and 1” up to 164psf. That means a 1’x3’ shelf of 1/4” plywood could carry about 15lbs, 1/2″ around 105lbs, 3/4″ 240lbs, and 1” ply up to 492lbs.
Most plywood-covered joist-supported floors are rated for 10 or 20psf of dead load and a live load of 30 to 40psf. That translates into a total load capacity between 40 and 60psf, so that loaded bookshelf might need to be strategically placed to prevent structurally damaging the floor. This may be why most such shelves are located at perimeter walls and close to structural supports.
What Does Affect Plywood Strength?
The amount of weight plywood can hold depends on several factors. The number and thickness of the plies or layers, the wood species, density, type of adhesive used, how it is fastened to supports, the unsupported distance, and the duration of the load all affect its holding power. Additionally, its orientation, whether the plywood is flat or on edge, is also important.
1. Wood Species
Plywood is commonly manufactured using thin layers of wood veneer laminated so that the grain of each sheet is perpendicular to the previous layer. Softwood is often used to make construction grades of plywood and comes in varying thicknesses and number of layers. Hardwood plywood is often used for furniture and architectural design elements, and decorative plywood for cabinetry, design elements, and furniture.
The wood species affects the strength of the plywood and its density. Softwoods typically have a lower density than hardwoods, so softwood plywood is not as strong as panels made of hardwood. They are also less expensive and thus more readily available.
Most common softwood species have a density between 25 and 30 lbs/ft³, while many hardwoods are in the mid to upper 40 lbs/ft³ and even higher. Exotic woods such as black walnut (63 lbs/ft³), mahogany (137 lbs/ft³), Brazilian Teak (220 lbs/ft³), and Brazilain walnut or Ipe (229 lbs/ft³) are denser and are often reserved for use as decorative plywood finishes.
Some softwood panels may have a higher-grade hardwood or softwood veneer on the outside or top face. Most hardwood panels have a core of hardwood and a top layer of premium-grade veneer. The higher-quality ply has fewer knots or blemishes, making it better for visible or decorative use.
The top face is often appearance graded AA, B, C, D, or E with AA having no visible defects and E containing the most defects. The back ply or face is also graded but numerically for strength from 1 to 4 with 1 being the higher quality or strength and 4 the lowest. The higher the grade, the higher the price, so depending on the project, consider B or C-grade plywood.
2. Number of Layers
The number of layers affects the quality and cost of the plywood and its load capacity. A 3/4″ plywood with 5 layers is strong, but a 3/4″ panel with 7 or more layers is stronger. The greater number of layers per thickness makes the lamination stronger. Each layer has an alternate grain orientation perpendicular to the one above or below plus more glue to bond the layers. The alternating grain pattern improves the strength, flexibility, and bearing capacity.
The minimum number of plies is three, a top and bottom veneer layer and a single core layer. Layers are commonly 1/8” or 1/10” thick, but higher quality panels have thinner layers. Plywood also usually has an odd number of layers, which helps reduce warping and balances the board.
The thickness of each core ply is usually the same, while the top and bottom veneer layers may be thinner. However, in most softwood building grade plywood the top and bottom layers are often the same thickness as those that make up the core. Some plywood can have as many as 21 or 23 layers, making it extremely strong.
3. Grain Direction
Plywood is made up of thin layers or plies of wood that are glued, heated, and pressed together. The grain direction of each layer is perpendicular to the ply below and above. This makes it stronger and more rigid, and less likely to warp or bend than solid wood of the same thickness.
When using plywood for roofing or flooring, the top layer’s grain is usually perpendicular to the joists or rafters. When used on walls, the top layer grain can run in either direction.
4. Type of Glue
There are two main types of glue used to bond plywood layers together. The most common is urea formaldehyde which is a synthetic aminoplastic resin glue made of urea and formaldehyde. It cures hard, is moisture resistant, and has a long history of reliability.
The other less toxic but more expensive bonding agent is phenolic glue, a synthetic polymer made from phenol and formaldehyde. It is more water resistant and sets rigid and hard, and is often used for exterior applications.
A third type is made using melamine, urea, and formaldehyde or MUF resins, but it isn’t as long-lasting as the other adhesives. Regardless of the type of glue, it is evenly spread on each layer, then cold pressed to form panels before being hot pressed to set and cure the glue.
The thickness of the plywood affects its strength, the same as the thickness of most structural materials. A 1/4” thick sheet can carry 5psf while a 1/2” will hold up to 35psf, a 3/4″ 80psf, and 1” about 164psf, so thickness does affect strength. Additionally, the thickness and number of layers also affect panel strength. A 5-ply 1/2″ sheet of plywood is not as strong as 1/2″ plywood with 7 or 11 plies.
Plywood Strength Chart
There are many variables that affect the strength of plywood. The species of wood, types of glue, grading, and thickness, plus the thickness and number of layers all impact plywood’s strength. Additionally, the orientation, use, and span also affect the strength too.
The table below identifies the maximum load for different thicknesses of softwood plywood. Some panels of the same thickness will support less, others more. Please note, the fewer number of plies per thickness typically means the lower its strength.
|Softwood Plywood Strength|
Plywood Load Capacity Calculator
There are numerous plywood load capacity calculators available online. However, some require more information than others, which could be problematic, but give a more accurate answer. Some calculators presume the plywood is fastened at the ends and that the top grain is perpendicular to the supports, as well as other factors.
Most, though, provide a ballpark load that shouldn’t be used for structural calculations – for those, talk to a Structural Engineer. Our pick for a simplistic estimate for common thicknesses is Plywood Load Capacity Calculator – Calculator Academy. Just input the length and width, select the thickness as a decimal, and press ‘Calculate’.
Plywood Bending Strength
Plywood bending strength depends on its thickness, wood species, number and thickness of layers, and the distance it spans, plus how and where it is fastened and other variables. A force applied to the top of the plywood causes compression to occur in the top plies or layers and torsion in the bottom layers. Plywood tends to resist deflection or bending well because the different layers split the resistance between the top and bottom.
Bending typically occurs when a static weight remains in place, or a force is applied that exceeds the maximum bearing load of the materials from which the plywood is fabricated. Resistance to bending improves if the ends or edges are nailed to supports. Softwood will bend easier than hardwood plywood too.
Most plywood bears “Span Rating” stamps on the bottom face that identify the maximum center-to-center span a panel is recommended for 16”, 20”, 24”, 32”, or 48”. The span rating may be two values separated by a slash mark, such as 32/16 or 48/24. The greater the span rating, the stiffer and stronger the plywood. The stamp also identifies the panel’s thickness as a decimal, its grade or end use designation, and the wood species group number classifying its strength.
Is Plywood Stronger Than Wood?
Plywood is made from thin layers of wood peeled off logs called peelers. The thin layers or plies are assembled so that each layer’s grain is perpendicular to the one above it, thus the grain goes in two directions. The plies are bonded together with adhesives, which combined with the cross-directional grain layering, results in a strong, sturdy panel that resists bending, warping, and twisting. The species of wood the layers are taken from also affects the strength, use, and cost.
Lumber is cut from logs, so the wood grain is all in one direction. Much depends on where it is cut from the log and how it is cut – plain, quarter, rift, or live sawn. Lumber is more susceptible to cupping, twisting, or warping based on the orientation of the growth rings – which are flattened in plywood – and the unidirectional grain. Softwood is less dense than most hardwoods, isn’t as strong, or as expensive, and is more commonly used in building and manufacturing.
Plywood typically provides a more uniform thickness, covers a larger area, and is less likely to bend, split, or break. However, it is more expensive to manufacture than milling lumber of the same species. Lumber, though, is all one homogeneous material, is typically heavier and denser when compared to plywood of similar size and species, and thus is considered stronger.
It is easier to say plywood is at least as strong as lumber of the same thickness. Much though, depends on the density of the wood used in the plywood and the wood it’s being compared to, plus what it’s being used for. Driving a nail into the edge of a stud results in a strong connection. Driving a nail into the edge of plywood will typically split the wood resulting in a poor connection.
Is Plywood Stronger Than MDF?
MDF is manufactured using hard and softwood fibers and adhesives that are blended together and then heated and pressed into forms to create medium-density fiber (MDF) boards. The panels are smoother than plywood and accept paint better. Although less susceptible to weather changes than plywood, if MDF gets wet, it can turn to mush.
The lack of grain direction makes MDF less durable and weaker than plywood in some situations. When oriented flat, MDF will sag easier, but if vertically oriented it is typically as strong or stronger than plywood. However, MDF will require reinforcement to maintain its rigidity.
Available in similar thicknesses to plywood, MDF panels are denser and heavier, and less expensive. Plywood has better holding strength for fasteners and is more flexible and less susceptible to breakage or splitting.
How to Make Plywood Stronger?
Unless you’re a plywood mill owner/operator and can affect changes in plywood manufacture, we’re looking at ways end-users can strengthen plywood. Some manufacturers use specially blended exterior grade adhesives to bond softwood plies together, making them less susceptible to moisture changes, and thus stronger. So, applying waterproof paint or clearcoat to the exposed surfaces will also reduce moisture absorption and make plywood stronger.
Reinforcing plywood shelves or countertops with solid wood or plywood strips at the edges helps prevent bending. Apply a thin layer of quality PVA (polyvinyl acetate) glue to matching faces and clamp them together until dry. Alternatively, miter the plywood edge and glue and clamp a strip of plywood or solid wood that is also mitered to the edge. This will strengthen the horizontal plywood and also hide the exposed plywood layers, making them stronger and easier to finish.
Another way is to double up the plywood fully in the same way as a shelf but for vertical use, making it thicker and stronger. Depending on the end use, some suggest sandwiching a layer of fiberglass cloth in resin between the two laminated pieces of plywood to further improve strength.
Is Plywood Stronger Than OSB?
OSB, or oriented strand board, is made of thin strands or wafers of wood saturated in a mixture of wax and adhesives. Up to 50 layers of strands are used to make the panels. Small stands oriented one way make up the core and larger strands oriented perpendicular to the core make up the top and bottom layers, making the panels more stable.
The outer layers usually are oriented in the direction of use. The mass of layers is about 8” thick before they are heated and pressed, bonding them into the desired panel thickness before being trimmed, sanded, and finished.
Both OSB and plywood of similar thicknesses are approved for use as structural panels to sheath floors, walls, and roofs. Both are rated to span similar distances and have common fastener pull-through strength. In the area of shear strength, however, OSB has a slightly higher rating than plywood of the same thickness.
OSB also has a more consistent thickness, no soft spots or voids like plywood may, and a more uniform density. Plywood is smoother, easier to sand and finish, and doesn’t swell and flake like OSB if exposed to moisture.
What Is the Strongest Plywood?
Marine plywood or APA Marine Grade Plywood is considered the strongest plywood. It is manufactured from 9 to 21 or more thin layers of fine-grained high-quality Douglas fir or western larch in the same manner as other plywood. However, it has more layers than common plywood, no voids or soft spots, and a strong waterproof glue is used to bond the plies together.
Marine plywood commonly has a thin non-counted hardwood or exotic high-grade veneer applied to the top and bottom. The larger number of thin fine-grained plies, coupled with the waterproof glue, make marine plywood stronger, more durable, and resistant to insects, rot, and decay.
Marine grade plywood is engineered for use in high moisture environments and to withstand direct water contact. It is not waterproof, but the waterproof glue helps prevent moisture penetration and applying waterproof paint or varnish protects the outer surface.
APA marine grade panels are high grade, so available in only AA, AB, and BB designations. They are typically available in eighth-inch increments from 1/8” up to 1-1/4” thicknesses, and in 4×8 and 5×5, 5×10, 5×12, and 6×12 sheets. It can also be specially ordered in other dimensions and thicknesses.
Plywood is a strong engineered wood that has many uses. It’s available in a variety of thicknesses and sheet sizes but is most commonly sold in 4’x8’ panels. Plywood gets its strength from the multiple plies with alternating grain directions bonded together with a strong durable glue. The number and thickness of the plies and the wood species used along with other factors affect its strength too.
Depending on the various factors, 1/4” softwood plywood can hold 5psf, 1/2″ 35psf, 3/4″ 80psf, and 1” approximately 164psf. The more plies per thickness, the stronger the plywood. Hopefully, you have a better understanding of what affects the strength of plywood, and how much it can hold, and are better prepared for your plywood-using projects.