Two standards, one sheet. Where the bands actually differ, and why a stated millimetre figure beats a cited standard on a purchase order.
Both systems are legitimate; what matters is that the contract names one. EN 485-3 covers thickness, width and form tolerances for hot-rolled sheet in the European system; ASTM B209 does the same job in the US system. They are close but not identical — the thickness tolerance bands, the width allowances and the flatness wording differ, and a drawing that cites both without saying which governs leaves the mill to pick. Put one standard on the order and add "or equivalent by agreement" only if you mean it.
This question arrives when a European specification is being bought in Asia, or a US specification is being quoted from a mill that works to GB/T. The material is the same; the paperwork is not. Once the standard is fixed, the tolerance table becomes a checkable number rather than an argument at goods-in.
EN 485 is a multi-part standard: part 2 covers mechanical properties, part 3 tolerances on dimensions and form for hot-rolled products, part 4 the same for cold-rolled. ASTM B209 is a single specification covering aluminium sheet and plate, with tolerance tables embedded in it. In practice a buyer compares part 3 or 4 against B209's dimensional tables.
| Item | EN 485-3 / 485-4 | ASTM B209 | Practical effect |
|---|---|---|---|
| Thickness tolerance | Banded by width and thickness range | Banded by width and thickness range | Bands differ near the edges of a range — check the actual table |
| Width tolerance | Separate table for slit and sheared edges | Covered in the same dimensional table | Slit edge vs sheared edge is where quotes diverge |
| Flatness | Expressed as deviation over a length | Expressed as deviation over a length | Both need a stated measuring method to be enforceable |
| Squareness / edge | Tolerances on out-of-square | Tolerances on out-of-square | Rarely quoted, frequently the complaint |
| Mechanical properties | EN 485-2 | In B209 itself | A 3.1 certificate should name which one |
The point of the table is not that one system is tighter. It is that the two cannot both govern, and the differences show up exactly at the limits where a buyer is most likely to measure.
Whichever the purchase order names. A mill that works daily to GB/T can supply to EN 485 or B209 — the rolling is the same, the inspection record changes. What it cannot do is guarantee both simultaneously when they conflict.
Our own default when a customer has no preference is to state the thickness tolerance explicitly in millimetres on the quotation rather than to cite a standard and let the reader look it up. That sounds less official and works better: "2.0 mm ±0.10 mm, measured at five points per sheet" is a sentence two parties can agree on without opening a standard.
Because weight and stiffness both follow the actual thickness, not the nominal one. A 2.0 mm sheet at the bottom of its tolerance band is about 5 % lighter than one at the top — which is 5 % less metal, 5 % less stiffness and, over a container, a real difference in what you paid for. This is the reason thickness is measured at five points per sheet rather than once, and why the measurement record is worth keeping.
The same logic applies to the film: a 50 µm sheeting at the low end of its band is a different product from one at the high end, even though both are "50 µm".
One standard, one thickness tolerance in millimetres, one measuring method, one flatness figure. Four lines. Everything the mill needs to decide, and everything you need to reject a delivery without an argument.
EN 485-3, "Aluminium and aluminium alloys — Sheet, strip and plate — Part 3: Tolerances on dimensions and form for hot-rolled products", is published by CEN. ASTM B209, "Standard Specification for Aluminum and Aluminum-Alloy Sheet and Plate", is published by ASTM International. Both define dimensional tolerances; only one can govern a given order.
Sources: CEN, Brussels · ASTM International, West Conshohocken, PA. Cited 30 October 2026.
It can state compliance with both where the requirements do not conflict, and many mills do. Where they differ, the certificate should say which one the values were judged against — otherwise the document is not evidence of anything specific.
Neither is uniformly stricter. The bands are drawn differently, so for a given thickness one system may allow slightly more and the other slightly less. Compare the actual table rows for your thickness and width rather than the standard as a whole.
It means the supplier is offering to hold half the permitted deviation — for example ±0.05 mm where the standard allows ±0.10 mm. It is a commercial commitment beyond the standard, and it belongs in the order as a number, not as a phrase.
No. Thickness and tolerance do not change the heading; product form and alloy family do. The standard citation belongs in the technical file, not on the customs declaration.
Specification questions are answered by the same person who quotes the job.