Plywood sheets vary in composition and thickness. However, the width and length of plywood is standardized at 48 by 96 inches to aid in planning and to comply with building codes. This standard width and length extends to all exterior, interior, soft and hardwood types of plywood in all thicknesses. Sizes other than the standard 48 by 96 inches are pieces that were cut after the plywood was manufactured.
Hardwood plywood is any plywood that is made from oak, ash, maple, birch, cherry, walnut or any other hardwood species. This type of plywood is always manufactured in the standard 48-by-96-inch sheets but is available in different thicknesses. For most cabinets and furniture construction, 3/4-inch hardwood plywood is used. For drawer sides, special bins and pull-outs, 1/2-inch plywood is available. For open-backed cabinets, china cabinet backs or drawer bottoms, 1/4-inch hardwood plywood is available. For special projects, 3/8-inch hardwood plywood is also manufactured but rarely used. All hardwood plywood is cut to width and length from a 48-by-96-inch sheet.
Softwood plywood is made almost exclusively from fir. This type of plywood is used mostly for interior structural building where the plywood is not visible. If the plywood is visible, it is always painted to hide varied defects that are common in softwood plywood. Softwood plywood sheets are also standardized at 48 by 96 inches and are available in 3/4-inch, 5/8-inch, 1/2-inch and 1/4-inch thicknesses. Softwood plywood is an affordable alternative to hardwood plywood and is often used on garage or shop cabinets. Occasionally, 1/4-inch softwood plywood is used as a sheathing, paneling on interior garage walls. 5/8-inch plywood is also used as floor underlay.
Exterior plywood is also standardized at 48 by 96 inches with varying thicknesses available. Exterior plywood is made with waterproof glue and resists moisture penetration. Exterior plywood is available in 1-, 3/4- and 5/8-inch thicknesses. 1-inch exterior plywood is used for concrete framing, stair treads and other applications where extra strength is required. Flooring applications utilize 3/4- and 5/8-inch-thick plywood. Sheathing (which is an exterior application on studs), sub-floors, and transoms and dormers (which are aesthetic architectural additions), all utilize exterior plywood cut to size from 48-by-96-inch sheets.
There are exceptions to all of the standard sizes of plywood. For example, even though plywood is referred to as 3/4- or 1/2-inch, manufacturers have altered these sizes. It is not uncommon for 3/4-inch plywood to measure at a thickness of 11/16 inch. Even though it is common to refer to it as 3/4-inch, it is actually 11/16 inch in thickness. This is a common size and completely acceptable. This concept is applied to all of the differing thicknesses. If the plywood measures 1/6 inch less than its stated measurement, it is standard procedure and is okay to use.