Plywood thickness converter
Plywood size names to stamp categories, labels and actual ranges, or a measured thickness back to its category, in inches and mm.
Start from
Surface
Size name
Inches or mm, such as 0.70, 17.8 mm or 23/32.
Called 3/4"
23/32 category
Labeled .703" (17.9 mm). Unsanded, it can measure 0.688" to 0.750".
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The true 3/4 category is labeled .734" (18.6 mm), 0.719" to 0.781" unsanded. Check the stamp for which one a sheet is.
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What the answer means
The category is the fraction on the panel’s stamp, linked to the thickness names in the US building codes. The label is the thickness in thousandths of an inch printed with it, and the range is how far a real sheet may sit from the category. That allows up to 1/32" either way for unsanded panels through 13/16, and 1/64" for sanded panels through 3/4.
Measuring a sheet
PS 1 measures thickness with a micrometer at the middle of each edge and averages the four readings, moving off any knot or patch that changes the thickness. Four caliper readings taken the same way, averaged, give the number to enter. Unsanded readings from 0.719" to 0.750" fit inside both 23/32 and 3/4, so for those the stamp is what tells the two apart.
Hardwood and metric sheets
Cabinet-grade hardwood plywood follows HP-1, and PS 1 is a US standard, so for those sheets a reading only shows which PS 1 range it falls in. See the plywood thickness chart for every category side by side.
Common questions
How do I convert plywood thickness to mm?
Multiply the inches by 25.4. The 23/32 label, .703 inch, is 17.9 mm, and the 15/32 label, .451 inch, is 11.5 mm.
Is 18mm plywood the same as 3/4 inch?
Not exactly. 18 mm is 0.709 inch, inside PS 1's 23/32 range (0.688 to 0.750 inch unsanded) and under the 3/4 category's 0.719 inch minimum. Sheets made to metric standards outside the US aren't covered by PS 1.
Which is thicker, 19/32 or 5/8 plywood?
5/8. Its label is .609 inch (15.5 mm) against .578 inch (14.7 mm) for 19/32, though unsanded panels of the two can overlap between 0.594 and 0.625 inch.
Where we get our information from
Categories, ranges and labels are from PS 1-22 (Table 10 and Appendix D), and Georgia-Pacific’s published decimals match the labels. Millimetres are worked out from inches, to 0.1 mm. Checked against published data from NIST, USDA Forest Products Laboratory and Georgia-Pacific.
See all 3 sources
- NIST, Voluntary Product Standard PS 1-22, Structural Plywood (2023)
- USDA Forest Products Laboratory, Wood Handbook (FPL-GTR-190, 2010), chapter 11, wood-based composite materials
- Georgia-Pacific, Plytanium Plywood Rated Sheathing (product page and specification sheet)
These are PS 1 ranges for US structural plywood. Which panel a floor, roof or wall needs comes from its span rating and the local building code.