Thickness tolerance in acrylic
“3 mm” on the sheet is a nominal dimension, not a measurement. How far the real thickness may deviate from it depends on the manufacturing process — and decides whether your tab joint fits.
Reviewed on 11 September 2026
AI-generatedAcrylic is sold by nominal thickness: 2, 3, 4, 5 mm. No sheet is exactly that thick. How far it may deviate is standardised — and differs greatly depending on the manufacturing process.
For a sign it does not matter. For anything that slots together — tab in slot, finger joints, grooves, stacked layers — the sheet thickness is the second dimension of the joint. If it is off, even the most accurate drawing will not help.
What the standards permit
| Material | Permitted deviation | Example |
|---|---|---|
| Cast acrylic (GS) | ± (0.4 + 0.1 × thickness) mm | 3 mm: 2.3 to 3.7 mm |
| Extruded acrylic (XT), 1.5 to under 3 mm | ±10% | 2 mm: 1.8 to 2.2 mm |
| Extruded acrylic (XT), 3 mm and above | ±5% | 3 mm: 2.85 to 3.15 mm |
| Precision cast acrylic (GS) | ±0.1 mm | 2 mm: 1.9 to 2.1 mm |
GS to ISO 7823-1, XT to ISO 7823-2 — where the tolerance explicitly applies within a sheet and from sheet to sheet. Precision acrylic according to the material information in our range.
Cast acrylic by thickness
| Nominal thickness | Tolerance | Permitted thickness |
|---|---|---|
| 2 mm | ±0.6 mm | 1.4 to 2.6 mm |
| 3 mm | ±0.7 mm | 2.3 to 3.7 mm |
| 4 mm | ±0.8 mm | 3.2 to 4.8 mm |
| 5 mm | ±0.9 mm | 4.1 to 5.9 mm |
| 6 mm | ±1.0 mm | 5.0 to 7.0 mm |
| 8 mm | ±1.2 mm | 6.8 to 9.2 mm |
Limits set by the standard, not typical values — not every sheet uses them up. You still have to design for the limit.
Why cast acrylic varies so much
GS is made by pouring liquid PMMA between two glass plates, where it cures. How thick the sheet ends up is determined by the gap between the plates and the shrinkage during curing — neither can be controlled to a tenth of a millimetre.
XT, by contrast, is forced through a die as a melt and brought to thickness between rollers. That keeps the thickness considerably more uniform, and the standard is correspondingly stricter: ±0.15 instead of ±0.7 mm at 3 mm.
What this means for a tab joint
A slot for 3 mm acrylic, drawn 3.0 mm wide, only fits if the sheet really is 3.0 mm thick. With cast material, however, the tab may be up to 3.7 mm thick — then it will not go in. Or it is only 2.3 mm thin and has 0.7 mm of play. Both are within the standard.
On top of that comes the kerf: the laser widens every slot by its own beam width. Thickness tolerance and kerf add up — how to design the slot for both is shown in the article on kerf.
Three routes to a joint that fits
- Design the slot for the upper limit of the tolerance and fix the part with adhesive or a screw instead of relying on a press fit.
- Order a sample piece, measure the actual thickness and design the slots accordingly. With cast acrylic, however, that measurement only applies to this one delivery.
- Choose precision acrylic or XT if the joint has to fit without rework and across several orders.
Precision acrylic: when it is worth it
Precision cast acrylic (GS) is cast acrylic manufactured to a thickness tolerance of ±0.1 mm. At 2 mm the sheet therefore reliably lies between 1.9 and 2.1 mm — ordinary cast acrylic of the same thickness may lie between 1.4 and 2.6 mm.
We stock it in 0.5, 1 and 2 mm, and that is no coincidence: with thin layers in particular, a coarse tolerance weighs most heavily in relative terms. Typical cases are stacked layers in which the deviations add up, and spacers and inlays that are meant to sit flush in a groove.
Two limitations come with it: precision acrylic costs more than standard GS of the same thickness, and it only tolerates light to medium engraving — 1 mm material engraved over large areas often no longer lies completely flat, and on 0.5 mm we advise against engraving altogether.
And XT?
Extruded acrylic (XT) is the middle way: at most ±5% from 3 mm upwards, so 0.15 mm off at 3 mm — not quite as tight as precision acrylic, but almost five times more accurate than cast. In return it engraves with less contrast and is more sensitive to stress cracking; the full trade-off is in the article on GS and XT.
Frequently asked questions
- How close to 3 mm is 3 mm acrylic really?
- Under ISO 7823-1, cast acrylic (GS) may deviate by ± (0.4 + 0.1 × thickness) mm, so at 3 mm it may lie between 2.3 and 3.7 mm. Extruded XT from 3 mm upwards only by ±5%, i.e. 2.85 to 3.15 mm.
- What is precision acrylic?
- Cast acrylic manufactured to a thickness tolerance of ±0.1 mm. We stock it in 0.5, 1 and 2 mm — for joints and layers that have to fit without rework.
- Why does my tab not fit into the slot?
- Usually the sheet is thicker or thinner than its nominal size, and the kerf comes on top of that. With cast acrylic, the permitted deviation at 3 mm is ±0.7 mm — more than the kerf itself.
- Is XT more accurate than GS?
- In thickness, yes: the standard permits ±5% for extruded acrylic from 3 mm upwards, and ±0.7 mm for cast acrylic at 3 mm. On the other hand, GS engraves with more contrast and is more forgiving when gluing.
Read on
Sources
- ISO 7823-1 (cast PMMA sheets) and ISO 7823-2 (extruded PMMA sheets), each in the section on thickness
- Material information in our range on precision cast acrylic (GS)
- ISO 7823-1: Poly(methyl methacrylate) sheets — Part 1: Cast sheets (retrieved 11 September 2026)
- ISO 7823-2: Poly(methyl methacrylate) sheets — Part 2: Extruded sheets (retrieved 11 September 2026)