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IN BRIEF
Plywood thickness tolerance
Nominal plywood thickness is the ordered target; the offered tolerance defines the permitted variation around it. For a slot, groove or fitting, compare measured thickness with the mating part as well as the nominal label. Agree the measurement method, locations and acceptance range, then retain individual results with the panel reference so your production team can see the variation that affects assembly.
- Agree the requirement before judging the measurements.
- Record where and how each reading was taken.
- Keep raw readings with the component trial.
For the wider buying schedule, use the plywood size and thickness guide to select a format and organise item quantities before applying this measurement plan.
UNDERSTAND THE DETAIL
Nominal vs actual plywood thickness: what should you measure?
Nominal thickness is the product’s stated size. Measured thickness is the reading taken using the agreed method. Put the acceptable range from your drawing or order beside both values.
Three-quarter inch converts to 19.05 mm. If the quotation offers 18 mm, check the fit with the designer before fixing tooling or slot sizes, and record the agreed change.
- 1/4 inch
- 6.35 mm after unit conversion; confirm the offered panel tolerance separately.
- 1/2 inch
- 12.7 mm as a unit conversion; check the specified finished joint.
- 3/4 inch
- 19.05 mm as a unit conversion; distinguish it from an 18 mm item.
Should a slot be cut to the nominal panel thickness?
A slot must be sized for the required finished fit, not copied directly from the panel’s nominal thickness. Use the intended fit, measured panel range and actual machining process to establish the slot. Trial a representative joint before approving production. Record clearance or interference requirements separately from the panel measurement so later changes can be traced to the correct part of the assembly.
Continue with cabinet joint and hardware trials.
FROM THE REPORT TO YOUR MACHINING BRIEF
See the measured thickness beside the nominal size.
Start with a dimensional record, then match the offered panel to your slot, rebate or fitting. The ECQA inspection records 100% birch plywood at 2500 × 1250 mm in three nominal thicknesses. The SGS marine plywood report records a nominal 1220 × 2440 × 18 mm, 11-ply panel with dimensional test results.
All-birch plywood: retain both readings.
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| Nominal thickness | Thickness readings | Reading minus nominal | Diagonal difference |
|---|---|---|---|
| 21 mm | 21.09 / 21.05 mm | +0.09 / +0.05 mm | 1 / 1 mm |
| 24 mm | 24.10 mm | +0.10 mm | 1 mm |
| 30 mm | 30.21 / 30.10 mm | +0.21 / +0.10 mm | 1.5 / 1 mm |
“Reading minus nominal” is calculated from the recorded thickness. ECQA lists a dimensional criterion of ±1.5 mm and a diagonal-difference criterion of 2 mm. For a close-fitting component, put your required finished range on the drawing and agree the offered limits, measurement positions and machining stage with the quotation.
Read the full ECQA inspection report · See the birch shipment inspection
Marine plywood: keep the mean and the measurement method together.
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| Property | Report result | Test method |
|---|---|---|
| Mean thickness | 17.95 mm | BS EN 324-1:1993 |
| Length × width | 2441 × 1221 mm | BS EN 324-1:1993 |
| Squareness | 0.5 mm/m · Pass | BS EN 324-2:1993 |
| Edge straightness | 0.3 mm · Pass | BS EN 324-2:1993 |
The mean thickness is 0.05 mm below the nominal 18 mm description. For a hinge recess or slotted joint, also request individual readings at the working locations. Keep the sheet geometry with the cut list so trimming, grain direction and finished part sizes can be planned together.
Read the full SGS marine plywood report · See marine panel results and construction
Take the drawing into a practical next step.
Choose a material file for dimensional review, or a working piece for the actual joint. CUZI birch plywood is available in 3–30 mm; include your required gauge and fit with the request.
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| Buying task | Panel reference to retain | Continue |
|---|---|---|
| All-birch dimensional file | 21 mm · 1250 × 2500 mm · all-birch construction; add required lower/upper limits and measurement positions. | Request the 21 mm dimensional file |
| Raw-panel fitting trial | 18 mm · 1220 × 2440 mm · all-birch construction; add the actual slot, cutter and component drawing. | Try the 18 mm raw-panel joint |
| Finished-panel fitting trial | 18 mm · 1220 × 2440 mm · all-birch construction; review the clear-coated panel and mating opening at the finished stage. | Try the 18 mm finished joint |
| Marine cut-part dimensions | 18 mm · 1220 × 2440 mm · BS 1088 requirement; add the finished part sizes, tolerance and grain arrows. | Request the marine dimensional data |
Carry the same panel identity into the sheet-weight records and your receiving inspection. A revised gauge, finish or construction needs its corresponding fitting and weight line.
Agree how thickness will be measured
Put the drawing dimensions and units beside the nominal board thickness. Agree the finished tolerance with the supplier and try any close-fitting slot or rebate before ordering.
Agree the instrument, measurement locations, number of sheets and conditioning procedure with the parties evaluating the material. Record instrument identification and calibration status where required by the inspection plan. Use the same arrangement when comparing a sample with received material.
Turn the thickness request into a usable measurement schedule.
Choose the construction and the delivered stage before requesting a narrow thickness range. A raw sanded panel, an overlaid sheet and a coated component are different measurement items. Keep the actual offered limits and method beside the drawing requirement, with any coating or subsequent machining described separately.
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| Field | Define with the item | Use in selection |
|---|---|---|
| Material identity | Face/back, core/lay-up, model and material/drawing revision. | Compare measurements from the construction being offered. |
| Nominal and offered limits | Nominal description, required and offered lower/upper limits, units and raw/finished status. | Resolve any difference before the purchase and tooling are fixed. |
| Method and instrument | Named method/edition, instrument ID, contact arrangement, resolution and relevant calibration record. | Use a comparable procedure for the reference and delivered material. |
| Measurement conditions | Conditioning, moisture/temperature information where required, coating cure and measurement stage. | Compare the panel and mating detail under the agreed conditions. |
| Sheet and positions | Bundle/sheet ID, selected-sheet scope and marked position drawing. | Find the reading again and identify which material was examined. |
| Individual results | Each reading, units, minimum/maximum and relevant measurement uncertainty. | Retain an outlying position instead of replacing it with the average. |
| Joint requirement | Actual slot/rebate range, insertion/clearance or adhesive requirement, finished face and drawing revision. | Trial the full mating arrangement using the proposed panel. |
| Decision and handover | Agreed comparison rule, affected sheet/position, disposition and repeat-order reference. | Keep the inspection and fitting decision with the item and pack labels. |
EN 324-1 is a named wood-panel dimensional measurement reference. Where it is specified, use the required edition and procedure; the purchase still needs its applicable product limits and inspected scope. Agree how rounding and any reported uncertainty are handled near a limit. Instrument resolution and measurement uncertainty describe different things; NIST’s measurement uncertainty guidance explains the reporting basis.
Mark the viewing face, measuring origin and positions on a sheet sketch. Record the selected sheets and readings at edges, centres and critical fitting areas. Label any later change in measuring positions.
Keep variation visible in the record
Keep individual readings with their sheet and measuring position. This shows local fit variations that an average can hide. Note any coating or surface layer included in the measurement.
If the drawing is revised after the sample trial, revisit the acceptance record. A tighter joint may require different limits or a new sample. Keep any machining adjustment separate from a panel change so the revised offer still describes the material being purchased.
WORKED BUYING EXAMPLE
Example: compare a measured sheet with an agreed limit
Illustrative planning example; values and quantities are not product specifications or quotations.
This worked example uses a drawing range of 17.7–18.3 mm at agreed measuring positions. Use the tolerance in your own order when checking panels.
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| Item or observation | Record or compare | Next decision |
|---|---|---|
| Reading 1: 17.8 mm | Within the example limits. | Retain the position and sheet reference. |
| Reading 2: 18.2 mm | Within the same limits. | Check the representative joint as planned. |
| Reading 3: 18.5 mm | Outside the stated upper limit. | Identify the affected material and review against the agreed acceptance plan. |
What this means for the order
The three-reading average is about 18.17 mm, yet one position lies outside the example requirement. Report that difference instead of allowing the average to replace the agreed acceptance criteria.
Read each sheet’s range as well as its mean.
The following chosen readings use P1–P5 as labelled positions under one measurement plan and the same 17.7–18.3 mm limits. They show how to retain sheet identity and individual results; they are not CUZI measured lot data or a prescribed sampling plan.
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| Sheet | P1 / P2 / P3 / P4 / P5 | Minimum / maximum | Mean | Positions outside limits |
|---|---|---|---|---|
| T01 | 17.8 / 17.9 / 18.0 / 18.1 / 17.9 | 17.8 / 18.1 | 17.94 | 0 of 5 |
| T02 | 17.8 / 18.0 / 18.2 / 18.5 / 18.1 | 17.8 / 18.5 | 18.12 | 1 of 5 · P4 |
| T03 | 17.6 / 17.9 / 18.0 / 18.1 / 17.8 | 17.6 / 18.1 | 17.88 | 1 of 5 · P1 |
The three sheet averages are within the chosen limits. T02/P4 and T03/P1 need a closer look, so record their sheet and bundle numbers and agree any further checks on the remaining stock.
Choose the thickness around your component
CUZI birch plywood is available from 3–30 mm. A thickness choice should follow the drawing, machining process and required finished fit. When your tool setup needs a narrow range, send the lower and upper limits and ask for the tolerance offered for that construction before ordering.
Record a fit trial that the workshop can repeat
- Panel reading
- Record sample ID, sheet location, individual thickness and whether the panel is raw or finished.
- Mating part
- Record the actual slot or rebate width, cutter and drawing revision.
- Finished fit
- Check insertion, clearance, adhesive space and the effect of your coating using the intended process.
- Purchasing decision
- Keep the accepted panel range and tool arrangement together; repeat the trial if either changes.
For an inquiry, send the nominal thickness, critical joint detail, required limits and sheet quantity. Request a sample for machining rather than a face swatch when fit is the deciding factor.
Compare the finished thickness with the real slot range.
For this geometric comparison, use a chosen raw-panel range of 17.7–18.3 mm and an actual slot range of 18.4–18.6 mm. Then add a chosen 0.08–0.12 mm coating build on each broad face. These inputs demonstrate the dimensional relationship; the offered panel, actual finish and required fit are agreed for the part.
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| Panel stage | Panel thickness | Minimum clearance | Maximum clearance |
|---|---|---|---|
| Raw panel | 17.7–18.3 mm | 18.4 − 18.3 = 0.10 mm | 18.6 − 17.7 = 0.90 mm |
| Both faces coated | 17.7 + 0.08 + 0.08 to 18.3 + 0.12 + 0.12 17.86–18.54 mm | 18.4 − 18.54 = −0.14 mm | 18.6 − 17.86 = 0.74 mm |
Check the thickest finished panel against the narrowest slot, including coating build-up. Agree the required clearance, adhesive space and supports in the drawing. The ranges shown here compare the dimensional extremes.
When the slot is also painted, lined or otherwise finished, measure its remaining opening at the same stage instead of adding panel coating and keeping an unfinished slot value. Confirm actual cured thickness and assembly conditions with the workshop trial before changing the material or tool arrangement.
Take the measurement and mating detail into the inquiry.
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| Buying task | Record to keep | Continue |
|---|---|---|
| Raw-panel joint trial | Requested 18 mm nominal panel, actual offered range, slot/rebate and tool/drawing reference. | Request the raw-panel fitting sample |
| Finished-panel joint trial | Raw range, actual front/reverse finish, cured measurement stage and complete mating detail. | Request the finished-joint trial |
| Dimensional measurement file | Construction, method/instrument, positions, individual readings, limits and inspected scope. | Request the thickness measurement file |
| Thickness-controlled order | Required versus offered raw/finished range, retained fitting reference and supplied operations. | Quote the thickness-controlled item |
Keep these details with your inquiry
- Nominal thickness and required limits, in one unit.
- Instrument and agreed measurement positions.
- Sheet, bundle and sample references.
- Raw results, joint observations and the decision made against the requirement.
Review the relevant product guide and prepare your inquiry files.
Questions buyers ask
Is the nominal thickness an acceptance limit?
Not by itself. The purchasing description needs the applicable tolerance or drawing limits and an agreed method for evaluating them.
How many sheets should be checked?
Agree how many sheets to measure and how to select them for the order. The three readings here are a worked example of interpreting results.
Does a three-quarter-inch drawing mean an 18 mm board?
No. An 18 mm board is not the exact metric equivalent of 3/4 inch. Three-quarter inch converts to 19.05 mm. Keep the drawing’s actual nominal/category and required finished range with the offered product; resolve any proposed alternative before the joint and tool setup are fixed.
Should coating thickness be added before checking a joint?
Yes, when the joint is specified after coating; account for the actual cured coating on both mating parts. Compare panel and mating opening at the required finished stage. Include the actual face/reverse build and preparation; a finished slot may also have a different opening. Trial the cured assembly under the agreed conditions.
Can the average replace an out-of-range reading?
No. An acceptable average does not cancel an individual reading outside a specified local limit. Use the agreed limit and decision rule at the required positions. Retain each result and sheet identity; a mean describes the readings together and can hide an individual position outside the requirement.
What belongs in a dimensional measurement file?
Panel/model and construction, raw/finished range and method, instrument and contact arrangement, conditions, selected sheet/position identity, individual results and the agreed comparison rule. Keep the inspected scope and fitting reference visible.
What if my required range differs from the offered panel tolerance?
Resolve the construction, delivered processing stage and fitting requirement with the offer. Any change to material, machining or finish should be recorded with the revised drawing and repeated joint trial where it affects fit.
Does a positive calculated clearance establish an acceptable joint?
No. Positive geometric clearance alone does not establish an acceptable finished joint. It describes a geometric gap for the stated inputs. The finished assembly also needs its required insertion, adhesive, support, fastening and process conditions. Use the drawing and working trial to evaluate that detail.
Where can I read plywood thickness measurements?
The dimensional records show ECQA readings for 21, 24 and 30 mm all-birch plywood and SGS thickness, format and geometry results for an 18 mm marine panel. Open the corresponding report, then request the offered construction’s finished range and individual readings for your fitting detail.
