Plywood and Drywall Thickness: Nominal vs Actual

The real thickness of 1/4, 1/2 and 3/4 inch plywood, OSB and MDF, drywall thicknesses and where each goes, standard sheet sizes, and how to measure a sheet before you buy hardware or cut a dado.

Updated

Edges of plywood sheets drawn to scale showing the gap between nominal and actual thickness: 1/4 inch is 7/32, 1/2 inch is 15/32 and 3/4 inch is 23/32

Plywood is sold by a nominal thickness, a trade name that’s a little bigger than the real panel. A sheet of “3/4 inch” plywood usually measures 23/32 inch, and “1/2 inch” measures 15/32. It’s only 1/32 inch, but it’s enough to make a 3/4 inch dado sloppy or a hinge screw poke through. Drywall, by contrast, is made to its stated size.

Plywood thickness chart

Sold as Actual (in) Decimal mm Typical uses
1/8 in about 1/8 0.125 3.2 Craft, drawer bottoms, backer
1/4 in 7/32 0.219 5.6 Cabinet backs, drawer bottoms, paneling
3/8 in 11/32 0.344 8.7 Sheathing (some areas), underlayment, curved work
1/2 in 15/32 0.469 11.9 Wall and roof sheathing, shelving backs, jigs
5/8 in 19/32 0.594 15.1 Roof sheathing, subfloor at 16 in spacing
3/4 in 23/32 0.719 18.3 Subfloors, cabinets, shelves, furniture
1 1/8 in 1 1/8 1.125 28.6 Heavy subfloors at 24 in spacing, workbench tops

Actual sizes are for US construction and sanded plywood marked to the 32nd. Hardwood and imported plywood varies more: “3/4” birch is often 0.70 to 0.72 in, and metric sheets are sold as 6, 12 and 18 mm. Always measure the sheet you have before cutting joinery.

OSB and MDF

Panel Common thicknesses Notes
OSB sheathing 7/16 in (0.437 in), 15/32 in 7/16 is the most common wall sheathing
OSB subfloor 23/32 in, 7/8 in Often tongue-and-groove, “Edge Gold” or similar
MDF 1/4, 1/2, 3/4 in Made close to its stated size: 3/4 MDF is about 0.75 in
Particleboard 5/8, 3/4 in Close to stated size; shelving and cabinet boxes

Drywall thickness chart

Thickness mm Where it’s used
1/4 in 6.4 Covering old walls, curved walls
3/8 in 9.5 Remodeling over existing surfaces, double layers
1/2 in 12.7 Standard interior walls (and ceilings with “ceiling board”)
5/8 in 15.9 Ceilings, sound control, fire-rated (Type X) walls

Drywall sheets are 4 ft wide and 8, 10, 12 or 16 ft long; to work out the wall area in square feet first, use the square footage calculator. Hang them horizontally on walls in most homes: fewer joints to tape. For an attached garage, most US codes require at least 1/2 in drywall on the wall shared with the house and 5/8 in Type X on the ceiling if there’s living space above; check your local code.

Sheet sizes

Panel Standard size
Plywood, OSB, MDF 4 × 8 ft (48 × 96 in)
Hardwood plywood 4 × 8 ft; some 4 × 10 ft; imported 1220 × 2440 mm
Drywall 4 × 8, 4 × 10, 4 × 12 ft
Baltic birch 5 × 5 ft (1525 × 1525 mm)

Making DIY shiplap from plywood? The shiplap calculator works out how many plywood sheets to rip into shiplap strips for your wall.

How to measure a sheet

Measure the thickness at the edge with calipers, or hold a ruler flat against the edge and read to the nearest 1/32 inch. For a dado that fits, set the cut by the actual panel, not the nominal size: many router bits are sold as “undersized plywood” bits in 23/32 and 15/32 for exactly this reason. To convert between inches and mm, use inches to mm.

More DIY charts: lumber sizes: actual vs nominal · nail sizes · screw and bolt sizes · sandpaper grit.

Frequently asked questions

What is the actual thickness of 3/4 plywood?

Most 3/4 inch construction plywood is 23/32 in (0.719 in, 18.3 mm), about 1/32 inch thinner than its name. Hardwood plywood sold as 3/4 is often closer to 0.70 in, or 18 mm if imported. Measure before cutting a dado or buying hinges.

Why is plywood thinner than its listed size?

The listed size is a nominal or trade name. Panels are sanded and sized after pressing, and US product standards allow the actual thickness to be marked in 32nds, so a panel sold as 3/4 is stamped 23/32. It's the same idea as a 2x4 measuring 1 1/2 × 3 1/2 inches.

What thickness drywall for walls and ceilings?

1/2 inch is the standard for interior walls. Ceilings often use 5/8 inch, or 1/2 inch ceiling board, because it sags less between joists. 5/8 inch Type X is fire-rated: most US codes require it on a garage ceiling with living space above, while the wall between a house and an attached garage needs at least 1/2 inch.

Is drywall thinner than its listed size like plywood?

No. Drywall is made to its stated thickness: 1/2 inch drywall is 1/2 inch (12.7 mm). Only wood panels like plywood and OSB use nominal sizes that are thinner than the name.

What size is a sheet of plywood?

4 × 8 feet (48 × 96 inches) is the standard. Some sheathing and subfloor panels are cut 1/8 inch short in each direction so they can be spaced for expansion, and hardwood and cabinet plywood also comes in 4 × 10 ft and, imported, 1220 × 2440 mm.

More measuring guides