You are ordering stainless steel sheets. The specification says “2mm thickness.” But when you measure the sheet, it is 1.96mm. Is that acceptable? What is the allowed tolerance?

Thickness tolerance for stainless steel sheets is defined by ASTM A480 (North America) and EN 10088 (Europe). For a 2mm thick 304 cold-rolled sheet, the standard tolerance is ±0.09mm. Thinner sheets have tighter tolerances; thicker sheets have looser tolerances. Always specify the required tolerance when ordering.

I have supplied stainless steel sheets with standard and custom tolerances. A medical device manufacturer required ±0.05mm. A general fabricator accepted ±0.09mm. Let me walk you through thickness tolerance standards.

What is the thickness tolerance of a 316 stainless steel sheet?

The thickness tolerance for a 316 stainless steel sheet is the same as for 304. For a 2mm thick cold-rolled sheet, the ASTM A480 standard tolerance is ±0.09mm. For a 1mm sheet, it is ±0.07mm. For a 3mm sheet, it is ±0.11mm.

316 and 304 have identical thickness tolerances because the tolerance is based on the rolling process, not the grade. The values apply to both grades and to 316L/304L.

316 Stainless Steel Thickness Tolerance (Cold-Rolled Sheet, Width < 1,200mm ASTM A480)

Nominal Thickness (mm)	Tolerance (mm)	Example Range
0.3-0.5	±0.05	0.45-0.55 for 0.5mm
0.5-0.8	±0.06	0.74-0.86 for 0.8mm
0.8-1.0	±0.07	0.93-1.07 for 1.0mm
1.0-1.5	±0.08	1.42-1.58 for 1.5mm
1.5-2.0	±0.09	1.91-2.09 for 2.0mm
2.0-2.5	±0.10	2.40-2.60 for 2.5mm
2.5-3.0	±0.11	2.89-3.11 for 3.0mm
3.0-4.0	±0.13	3.87-4.13 for 4.0mm
4.0-5.0	±0.15	4.85-5.15 for 5.0mm
5.0-6.0	±0.17	5.83-6.17 for 6.0mm

My Experience
For a customer ordering 2mm 316 sheet, they measured 1.95mm and were concerned. I explained the tolerance is ±0.09mm (1.91-2.09mm). Their sheet was within tolerance.

What is the thickness tolerance for AISI 304 stainless steel sheets?

The thickness tolerance for AISI 304 stainless steel sheets follows the same ASTM A480 standard as 316. For a 2mm cold-rolled sheet, the tolerance is ±0.09mm. For a 1mm sheet, it is ±0.07mm.

The tolerance applies to both 304 and 304L. For hot-rolled sheets (No.1 finish), tolerances are larger. Always specify the required tolerance when ordering, especially for precision applications.

304 Stainless Steel Thickness Tolerance Table

Let me provide a complete thickness tolerance table for 304 stainless steel sheets.

Cold-Rolled Sheet (2B finish, width < 1,200mm), ASTM A480

Thickness (mm)	Tolerance (mm)	+ / -
0.5	±0.05	0.45-0.55
0.8	±0.06	0.74-0.86
1.0	±0.07	0.93-1.07
1.2	±0.08	1.12-1.28
1.5	±0.08	1.42-1.58
2.0	±0.09	1.91-2.09
2.5	±0.10	2.40-2.60
3.0	±0.11	2.89-3.11

Hot-Rolled Sheet (No.1 finish, thicker tolerances)

Thickness (mm)	Tolerance (mm)
3.0-5.0	±0.25
5.0-8.0	±0.30
8.0-12.0	±0.40

How to Measure Thickness

• Use a micrometer (accuracy ±0.001mm)
• Measure at least 10mm from the edge
• Take multiple measurements and average
• Remove any coating or oil before measuring

My Experience
For a precision part requiring 1.5mm thick 304 sheet, the customer specified custom tolerance ±0.05mm instead of standard ±0.08mm. The cost was 15% higher, but the parts fit perfectly.

What is the ISO standard for sheet metal tolerances?

The main ISO standard for sheet metal tolerances is ISO 9444 (for hot-rolled) and ISO 9445 (for cold-rolled stainless steel). These standards specify dimensional tolerances for continuously hot-rolled and cold-rolled stainless steel sheet and strip.

ISO 9445 covers cold-rolled stainless steel sheet with thickness from 0.3mm to 6mm. The tolerance classes are: Class 1 (normal) and Class 2 (precision). Class 2 tolerances are tighter than Class 1.

ISO 9445 Tolerance Classes (Cold-Rolled)

Let me provide the ISO 9445 thickness tolerances.

Class 1 (Normal Tolerance)

Thickness (mm)	Tolerance (mm)
0.3-0.5	±0.05
0.5-1.0	±0.07
1.0-2.0	±0.10
2.0-3.0	±0.13
3.0-4.0	±0.15
4.0-5.0	±0.18
5.0-6.0	±0.20

Class 2 (Precision Tolerance)

Thickness (mm)	Tolerance (mm)
0.3-0.5	±0.04
0.5-1.0	±0.05
1.0-2.0	±0.07
2.0-3.0	±0.09
3.0-4.0	±0.11
4.0-5.0	±0.13
5.0-6.0	±0.15

ASTM vs ISO Tolerance Comparison (2mm sheet)

Standard	Tolerance (mm)
ASTM A480	±0.09
ISO 9445 Class 1	±0.10
ISO 9445 Class 2	±0.07

My Experience
For European projects, we specify ISO 9445. For North American projects, we specify ASTM A480. The tolerances are similar but not identical.

What is the thickness tolerance of MS sheets?

MS (mild steel) sheet thickness tolerances are defined by ASTM A6/A6M. For a 2mm thick hot-rolled MS sheet, the tolerance is approximately ±0.2mm, which is looser than stainless steel sheet tolerances.

MS sheet tolerances vary by thickness and width. Hot-rolled MS sheet has looser tolerances than cold-rolled stainless sheet. For precision applications, cold-rolled MS sheet (thickness under 3mm) has tighter tolerances.

MS Sheet Thickness Tolerance (Hot-Rolled, ASTM A6)

Thickness (mm)	Tolerance (mm)
1.5-2.0	±0.2
2.0-2.5	±0.2
2.5-3.0	±0.2
3.0-4.0	±0.3
4.0-5.0	±0.3
5.0-6.0	±0.4

Cold-Rolled MS Sheet (Thickness under 3mm)

Thickness (mm)	Tolerance (mm)
0.5-1.0	±0.08
1.0-2.0	±0.10
2.0-3.0	±0.12

Stainless vs MS Sheet Tolerance Comparison (2mm)

Material	Standard	Tolerance (mm)
Stainless steel (304, cold-rolled)	ASTM A480	±0.09
MS (cold-rolled)	ASTM A568	±0.10
MS (hot-rolled)	ASTM A6	±0.20

My Experience
MS sheet tolerances are looser. For a 2mm MS sheet, the actual thickness could be 1.8-2.2mm. For stainless, it is 1.91-2.09mm. Stainless has tighter control.

Conclusion

316 and 304 stainless steel sheets have identical thickness tolerances. For 2mm sheet, ASTM A480 tolerance is ±0.09mm. ISO 9445 is the international standard for sheet metal tolerances. MS sheet tolerances are looser than stainless sheet tolerances.