Structural panels: Performance Category
Sheathing, subfloor and other structural plywood and OSB made to Voluntary Product Standards PS 1 and PS 2 used to be labelled by nominal thickness, with a tolerance that allowed a 3/4 in panel to be 1/32 in thin. Weights-and-measures labelling rules do not allow that, APA explains, so panels now carry a Performance Category — the nominal size the building codes use — and the category sets a thickness range:
| Performance Category | Minimum (in) | Maximum (in) | Minimum–maximum (mm) |
|---|---|---|---|
| 7/16 | 0.406 | 0.469 | 10.32–11.91 |
| 1/2 | 0.469 | 0.531 | 11.91–13.49 |
| 19/32 | 0.563 | 0.625 | 14.29–15.88 |
| 5/8 | 0.594 | 0.656 | 15.08–16.67 |
| 23/32 | 0.688 | 0.750 | 17.46–19.05 |
| 7/8 | 0.831 | 0.919 | 21.11–23.34 |
| 1 | 0.950 | 1.050 | 24.13–26.67 |
| 1-1/8 | 1.069 | 1.181 | 27.15–30.00 |
PS 2-10, Table 1, as quoted by Huber Engineered Woods: ±1/32 in on categories of 13/16 in and under, ±5% above. A '23/32 Category' panel — sold as 3/4 in — may measure anywhere from 0.688 to 0.750 in.
Metric and hardwood plywood
- Metric birch plywood is made to millimetre sizes. One maker's standard range is 4, 6.5, 9, 12, 15, 18, 21 and 24 mm and up, to the European tolerance standard EN 315. An 18 mm sheet is 0.709 in — close to, but not, 3/4 in.
- Hardwood and decorative plywood, the faced panels used for cabinets, is made in the United States to ANSI/HPVA HP-1, which sets its own grades and tolerances. They were not available to review, so no figures are given here.
- The label is not the measurement. Thickness also changes with the panel's moisture content.
Fitting grooves and dadoes to the sheet
Sizing a joint for plywood
Measure the sheet
With calipers, at several points along an edge; readings can differ along a sheet. Size a groove the panel must enter to the thickest reading.
Cut a test groove in scrap
At the measured width, and check the fit before cutting the parts.
Adjust, not force
Shim a dado stack, or cut with a narrower router bit and widen the groove in a second pass, until the panel slides in with hand pressure. Dado stacks are covered in dado blades.
Keep the parts together
Cut all the parts for one assembly from the same sheet, or measure each sheet.
Before cutting joints in plywood
- Sheet measured with calipers at several points
- Category or metric size read from the stamp or label
- Groove sized to the thickest reading
- Test cut in scrap from the same sheet
- Parts for one assembly from one sheet
- Sheet acclimatised to the shop before measuring
Sheets for a project are counted on the plywood calculator, and laid out on the cut list optimizer. Solid-wood sizes, nominal and actual, are on the lumber dimensions chart; grades and surfacing of solid lumber in the lumber guide; and grain in wood grain. The lumber family is mapped in choosing lumber.
Sources
Structural panel ranges are PS 2-10's as a manufacturer quotes them; the standards themselves were not reviewed directly. Hardwood and decorative plywood is made to ANSI/HPVA HP-1, whose tolerances were not available to review, so none are given. Metric sizes are one maker's; others may differ.
- 1.
What is the PS2 Performance Category? (HUB 9114), quoting PS 2-10, Table 1. Huber Engineered Woods, 2018.
Used for: PS 2-10 Table 1 as quoted by a panel maker: minimum and maximum thickness for each Performance Category from 7/16 to 1-1/8; ±1/32 in (±0.8 mm) on categories of 13/16 in and less and ±5% above; the Performance Category introduced because labelling regulations were not compatible with the earlier nominal-thickness tolerances; abbreviations PERF CAT, CAT and Category; panel thickness changing naturally with moisture conditions.
- 2.
Panel Thickness Tolerances and Labeling (Technical Topic TT-054). APA — The Engineered Wood Association, 2013.
Used for: NIST regulations for structural panels no longer allow the minus 1/32 in tolerance on nominal thickness used in earlier editions of PS 1 and PS 2; panels labelled by Performance Category and by thickness, with a table relating the two.
- 3.
Riga Ply birch plywood datasheet. Latvijas Finieris (Riga Wood), 2025.
Used for: A birch plywood maker's standard thicknesses — 4, 6.5, 9, 12, 15, 18, 21, 24 mm and up — with thickness tolerances to EN 315.
About this chart
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