If you buy aluminum sheet and plate, the tolerance table is where a quote either stands up or falls apart at inspection. This page gives the aluminum sheet thickness tolerance numbers for the two standards you will meet most — ASTM B209 (North America) and EN 485 (Europe) — so you can check a supplier's promise against a number instead of a description.
The key point before the table: the tolerance depends on both thickness and width. A 1 mm sheet 2,000 mm wide has a wider tolerance than the same 1 mm sheet 1,000 mm wide, because wide strip is harder to hold flat and uniform. Any tolerance quoted without its width band is incomplete.
Thickness tolerance, sheet and plate
The figures below are the standard (non-special) tolerances. Special tolerances are tighter and must be agreed and paid for — they are never assumed.
| Nominal thickness | EN 485-3 | ASTM B209 | GB/T 3880 |
|---|---|---|---|
| 0.5 – 1.0 mm | ±0.04 mm | ±0.04 mm | ±0.05 mm |
| 1.0 – 3.0 mm | ±0.06 mm | ±0.06 mm | ±0.07 mm |
| 3.0 – 6.0 mm | ±0.10 mm | ±0.10 mm | ±0.12 mm |
| 6 – 12 mm (plate) | ±0.20 mm | ±0.20 mm | ±0.25 mm |
| 12 – 50 mm (plate) | ±0.30 mm | ±0.30 mm | ±0.40 mm |
For thin sheet, ASTM B209 also expresses the tolerance as a percentage in places — roughly ±3% at 1.0–3.0 mm and ±4% below 1.0 mm — which is why you sometimes see both a millimeter and a percent figure on the same drawing.
The width band matters more than most buyers realize. A supplier's table often looks like this for ASTM B209:
| Nominal thickness | Width ≤ 1,000 mm | Width 1,000–1,500 mm | Width 1,500–2,600 mm |
|---|---|---|---|
| 0.2 – 0.5 mm | ±0.040 mm | ±0.050 mm | ±0.075 mm |
| 0.5 – 1.0 mm | ±0.050 mm | ±0.075 mm | ±0.100 mm |
| 1.0 – 3.0 mm | ±0.075 mm | ±0.100 mm | ±0.150 mm |
| 3.0 – 6.0 mm | ±0.150 mm | ±0.200 mm | ±0.250 mm |
| 6 – 12 mm | ±0.250 mm | ±0.350 mm | ±0.450 mm |
| 12 – 25 mm | ±0.350 mm | ±0.450 mm | ±0.550 mm |
Notice the pattern: the tolerance widens as the sheet gets thicker and as it gets wider. A 4 mm sheet in a 2,000 mm width carries ±0.250 mm, while the same 4 mm sheet in a 900 mm width carries ±0.150 mm.
Width, length and flatness
Width and length tolerances are deliberately asymmetric — almost always "+X / −0" — because the buyer needs to be able to trim to finished size and never come up short.
| Dimension | EN 485-3 | ASTM B209 | GB/T 3880 |
|---|---|---|---|
| Width ≤ 1,000 mm | +2 / −0 mm | +3 / −0 mm | +3 / −0 mm |
| Width 1,000–2,000 mm | +3 / −0 mm | +4 / −0 mm | +4 / −0 mm |
| Length ≤ 2,000 mm | +5 / −0 mm | +6 / −0 mm | +6 / −0 mm |
| Length 2,000–5,000 mm | +8 / −0 mm | +10 / −0 mm | +10 / −0 mm |
| Flatness (sheet) | ≤0.4% of length | ≤0.5% of length | ≤0.5% of length |
| Squareness | ≤1.0 mm / 100 mm | ≤1.5 mm / 100 mm | ≤2.0 mm / 100 mm |
Flatness is the one buyers forget. A sheet that is within thickness tolerance but out of flat will jam a laser cutter or press brake, and flatness is where the three standards genuinely differ — EN 485 is the tightest, at 0.4% of length against 0.5% for the others.
Why the two standards are not interchangeable
EN 485 and ASTM B209 describe the same physical product, but the numbers are not identical, and the differences are real at tight tolerances. The most common dispute is a drawing that cites ASTM B209 while the mill works to GB/T 3880 — the GB tolerance is usually slightly wider, and at inspection the material that "should have passed" fails.
The rule that resolves it: name one standard on the order, for properties and for tolerances. Do not leave it implied. If the drawing cites ASTM, the practical question is whether the mill can hold the ASTM table — often it can, but it needs to be told, because the default production route is its domestic standard.
When to specify special tolerance
- Tight-gauge work. Stretch-leveled sheet for laser cutting or printing, or foil where the gauge drives the barrier.
- Aerospace and semiconductor panels, where EN 485-3 special tolerances are the starting point.
- Anything that must feed automatically. A roll former or automated line needs flatness and squareness beyond the standard table.
Special tolerance costs more and takes longer; it is a deliberate specification, not a default. If your process tolerates the standard table, do not pay for special.
The checksum you can run on any quote
When a supplier quotes a tolerance, ask three questions and the answer has to come back as a number, not a phrase:
- Which standard — ASTM B209, EN 485, or GB/T 3880?
- Which width band — because the number changes with width?
- Sheet or plate — because plate tolerances are a different table above 6 mm?
A quote that cannot answer all three with numbers is a quote you will be arguing about at inspection. For the grade and temper tables that go with these dimensions, see the alloy reference pages. If you have a drawing with a tolerance callout, send it over — we will confirm which standard it actually holds against.