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Introduction

When buying hot rolled carbon steel sheet or coil, one of the most important dimensional questions is:
What is the acceptable thickness tolerance for hot rolled carbon steel?
The answer depends on the applicable standard, specified thickness, product width, and whether the order uses nominal thickness or minimum thickness.
For many ASTM carbon and structural hot-rolled steel sheet products, ASTM A568/A568M provides the general dimensional requirements, including thickness tolerances. ASTM A568 Table 4 covers hot-rolled sheet for carbon and structural steel, with tolerance values determined by both ordered thickness and specified width.
This guide explains the ASTM A568 hot rolled steel thickness tolerance table, acceptable thickness limits, nominal vs. minimum thickness, measurement rules, and what buyers should check when inspecting hot rolled carbon steel sheet, HR steel coil, A36 steel plate and other hot rolled carbon steel products.

1. What Is the Acceptable Thickness Tolerance for Hot Rolled Carbon Steel?

There is no single thickness tolerance that applies to all hot rolled carbon steel.
Under ASTM A568/A568M, the permitted thickness variation depends mainly on:

• Specified ordered thickness
• Product width
• Carbon or structural steel category
• Nominal vs. minimum thickness
• Applicable tolerance table
• Whether standard or restricted tolerances are specified

For standard hot-rolled carbon and structural steel sheet, ASTM A568 Table 4 provides thickness tolerances based on the ordered thickness and width.
For example, the tolerance for a narrow hot-rolled sheet can be different from the tolerance for a wider sheet of the same nominal thickness.
Therefore, a statement such as:
“Hot rolled steel has a ±0.3 mm tolerance.”
is not sufficient for an ASTM-based inspection.

2. ASTM A568 Hot Rolled Carbon Steel Thickness Tolerance Table

The following is a practical reference based on the ASTM A568/A568M Table 4 structure for hot-rolled carbon and structural steel sheet.

*The ASTM table expresses the tolerance according to the specified thickness and width. The complete table contains additional width and thickness ranges. The values above are provided as a quick reference; the applicable ASTM edition should be used for contractual acceptance.
For example, 0.010 in. ≈ 0.254 mm, while 0.012 in. ≈ 0.305 mm.
The important point is that ASTM A568 does not use one universal ± tolerance for every hot-rolled steel thickness.

3. Nominal Thickness vs. Minimum Thickness

This is one of the most important details when checking a hot rolled steel thickness tolerance.
ASTM A568 distinguishes between an order specified by minimum thickness and one specified by nominal thickness.

Minimum thickness specification

The tolerance is generally expressed as:
Tolerance over, no tolerance under
For example, if the specified minimum thickness is 6.00 mm and the applicable tolerance is 0.30 mm, the acceptable range can be interpreted as:
6.00 mm to 6.30 mm
The material cannot fall below the specified minimum thickness.

Nominal thickness specification

For a nominal thickness, the tolerance is divided between the upper and lower sides.
For example:
6.00 mm nominal ±0.15 mm
would give:
5.85–6.15 mm
The distinction is critical because the same numerical tolerance can produce very different acceptance ranges depending on how the purchase order defines thickness. ASTM A568 explicitly notes that its tolerance values are based on minimum thickness, while nominal-thickness tolerances are divided equally over and under.

4. How Is Hot Rolled Steel Thickness Measured?

Thickness measurement is not simply taken anywhere on the edge of the sheet.
ASTM A568 specifies measurement locations relative to the product edge. For the Table 4 configuration, thickness is measured at points away from the edge, with different minimum distances applying to cut edge and mill edge material.
This matters because the edge of a hot rolled steel sheet can have dimensional characteristics that are not representative of the usable material.
The standard also specifies requirements for the measuring micrometer, including minimum anvil and spindle dimensions, and states that pointed-tip micrometers are not suitable for the thickness measurement described by the table.
Therefore, when inspecting:
ASTM A36 hot rolled steel sheet
or
ASTM A572 hot rolled steel
the measurement method should be agreed upon before deciding whether a material is out of tolerance.

5. Why Does Hot Rolled Steel Have Thickness Variation?

Thickness variation is a normal issue associated with the hot rolling process.
Several factors can affect the final thickness, including:

• Rolling temperature
• Roll gap
• Rolling force
• Mill setup
• Material width
• Steel grade
• Coil position
• Crown and flatness
• Cooling conditions
• Equipment capability

Because hot rolled steel is processed at elevated temperatures and undergoes significant deformation, the finished product does not necessarily have the same dimensional precision as cold rolled steel.
This is why hot rolled steel thickness tolerance is normally wider than the tolerance achievable with many cold rolled products.

6. Does Steel Width Affect Thickness Tolerance?

Yes.
This is one of the most important points in the ASTM A568 tolerance table.
The specified width is one of the variables used to determine the permitted thickness variation.
For example, ASTM A568 Table 4 contains separate width ranges such as:

• Up to 15 in.
• Over 15 to 20 in.
• Over 20 to 32 in.
• Over 32 to 40 in.
• Over 40 to 48 in.
• Over 48 to 60 in.
• Over 60 to 72 in.
• Over 72 in.

The permitted thickness tolerance can increase as product width and thickness increase.
Therefore, when a buyer asks:
“What is the acceptable tolerance for 10 mm hot rolled steel?”
the question is incomplete.
A more accurate question is:
“What is the ASTM A568 thickness tolerance for 10 mm hot rolled steel at my specified width?”

7. ASTM A568 vs. ASTM A36: Which One Controls Thickness Tolerance?

This is another common source of confusion.
ASTM A36 is a material specification for carbon structural steel.
It defines requirements such as:

• Chemical composition
• Yield strength
• Tensile strength
• Elongation
• Product requirements

The dimensional tolerance can be governed by a referenced general requirements standard such as ASTM A6/A6M or A568/A568M, depending on the product form and applicable specification.
In other words:
ASTM A36 = material grade
ASTM A568 = general requirements for certain steel sheet products
The two should not be treated as competing thickness-tolerance standards.

8. Hot Rolled Sheet vs. Hot Rolled Plate Thickness Tolerance

Buyers should also distinguish between hot rolled steel sheet and hot rolled steel plate.
ASTM standards use different product classifications and dimensional requirements.
For example, ASTM A656/A656M is a specification for hot-rolled structural plate and refers plate produced from coil to the additional requirements of ASTM A6/A6M.
Therefore, you should not automatically apply an ASTM A568 sheet tolerance table to every hot rolled steel plate.
Before inspection, confirm:
Product form → Applicable ASTM specification → Applicable tolerance table
This is especially important for thicker materials.

9. What Is a Typical Acceptable Thickness Tolerance for Hot Rolled Steel?

For practical purchasing discussions, buyers often encounter tolerances around:

• ±0.20 mm
• ±0.25 mm
• ±0.30 mm
• ±0.40 mm
• ±0.50 mm
• Larger tolerances for thicker products

However, these numbers should not be treated as universal ASTM limits.
The actual acceptable thickness tolerance depends on:
Thickness + width + standard + tolerance type + product category.
For example, an ASTM tolerance of 0.012 in. is approximately:
0.305 mm
while:
0.016 in. ≈ 0.406 mm
This illustrates why simply saying “±0.3 mm” without identifying the applicable standard can be misleading.

10. Standard vs. Restricted Thickness Tolerance

Some steel orders require tighter dimensional control than the standard tolerance.
ASTM A568 includes supplementary requirements for restricted thickness tolerances, which must be specifically requested by the purchaser.
This means a buyer requiring tighter thickness control should not simply assume that the mill will automatically provide a restricted tolerance.
The purchase order should clearly state the required tolerance and applicable supplementary requirement.
For precision fabrication, this can be important for:

• Laser cutting
• CNC machining
• Automated fabrication
• Precision bending
• Structural assemblies
• Automotive components
• Equipment manufacturing

11. How Should Buyers Check Hot Rolled Steel Thickness?

A professional inspection should include:

Step 1 — Confirm the purchase specification

Check:

• Steel grade
• Standard
• Nominal thickness
• Minimum thickness
• Width
• Product form

Step 2 — Identify the applicable tolerance table

Do not use a generic ±0.3 mm rule.

Step 3 — Measure at the correct location

Avoid measuring directly at an inappropriate edge location.

Step 4 — Use a suitable micrometer

The measuring instrument should comply with the applicable standard's requirements.

Step 5 — Take multiple measurements

Measure at several points across the width and along the length/coil where appropriate.

Step 6 — Compare with the specified tolerance

Determine whether the measured values fall within the contractual acceptance range.

12. Example: How to Calculate Acceptable Thickness

Suppose a buyer orders:

Hot Rolled Carbon Steel Sheet
Nominal thickness: 10.00 mm

Assume the applicable purchase specification allows:
±0.30 mm
The acceptable range would be:
9.70–10.30 mm
But if the order specifies:
Minimum thickness: 10.00 mm
with a tolerance of:
0.30 mm over
the acceptance range becomes:
10.00–10.30 mm
These two specifications are not equivalent.
This is why the wording on the purchase order matters just as much as the numerical tolerance.

13. What Thickness Tolerance Should You Put on a Purchase Order?

A professional hot rolled carbon steel purchase specification should identify:
Product: Hot Rolled Carbon Steel Sheet/Coil
Grade: ASTM A36 / A572 / specified grade
Standard: Applicable ASTM specification
Thickness: 10.00 mm
Width: 1500 mm
Tolerance: ASTM A568/A568M applicable tolerance
Tolerance type: Nominal or minimum thickness
Inspection: Thickness measurement at specified locations
For tighter requirements, write the required restricted tolerance explicitly.
This eliminates one of the most common disputes between steel buyers and suppliers:
“The thickness is different from the nominal size, but is it actually out of specification?”
The answer can only be determined by comparing the measurement with the correct standard and tolerance table.

FAQ

1.What is the standard thickness tolerance for hot rolled carbon steel?

There is no single universal value. ASTM A568/A568M determines thickness tolerance according to specified thickness and width for covered hot-rolled carbon and structural steel sheet.

2.What is ASTM A568 thickness tolerance?

ASTM A568 provides dimensional tolerances for carbon, structural and high-strength low-alloy steel sheet. Its hot-rolled sheet tables define thickness tolerances based on product width and ordered thickness.

3.Is hot rolled steel allowed to be under nominal thickness?

It depends on whether the order specifies nominal thickness or minimum thickness. For minimum-thickness orders, the tolerance is generally over only, with no tolerance under the specified minimum.

4.Is 10 mm hot rolled steel always allowed to be 9.7 mm?

No. A 9.7 mm measurement is acceptable only if the applicable specification and purchase order allow a lower limit of 9.7 mm.

5.Does steel width affect thickness tolerance?

Yes. ASTM A568 thickness tolerance tables use both specified thickness and specified width.

6.Is ASTM A36 the same as ASTM A568?

No. ASTM A36 identifies a carbon structural steel grade, while ASTM A568 provides general requirements for certain steel sheet products.

7.Can buyers request tighter thickness tolerance?

Yes. ASTM A568 includes supplementary requirements for restricted thickness tolerances, which must be specified by the purchaser.

Conclusion

The acceptable thickness tolerance for hot rolled carbon steel cannot be determined from nominal thickness alone.
For ASTM products, buyers should check:
Steel grade + product form + ASTM standard + specified thickness + width + nominal/minimum thickness + applicable tolerance table.
For hot-rolled carbon and structural steel sheet, ASTM A568/A568M Table 4 is an important reference for standard thickness tolerances.
The key takeaway is simple:

• Do not judge a hot rolled steel sheet by comparing its measured thickness with the nominal size alone. Always compare the measurement with the applicable standard tolerance.

For buyers sourcing hot rolled carbon steel sheet, hot rolled steel coil, ASTM A36 steel, ASTM A572 steel, structural steel sheet or carbon steel plate, defining the thickness tolerance clearly in the purchase order can prevent costly inspection disputes and rejected shipments.