Steel Round Bar Sizes, Dimensions and Weight

Steel round bar is available in a wide range of diameters and lengths for machining, fabrication, construction, machinery manufacturing, and industrial applications. Choosing the correct steel round bar size is important because diameter, length, and weight directly affect material selection, machining requirements, transportation, and project cost.

This guide covers common steel round bar sizes, standard dimensions, weight per foot and per meter, and practical formulas for calculating round bar weight.

For buyers looking for available carbon steel round bar products, specifications, grades, and supply options, see our Carbon Steel Bar product category.

Steel Round Bar Sizes

Steel round bars are primarily specified by their diameter. Common sizes range from small diameters used for precision machining to large diameters used for shafts, structural components, and heavy industrial applications.

The following table shows common metric steel round bar sizes and their approximate theoretical weight based on a carbon steel density of 7,850 kg/m³.

Diameter (mm)	Approx. Inch Equivalent	Weight (kg/m)	Weight (kg/6 m)
10	0.394	0.62	3.70
12	0.472	0.89	5.33
16	0.630	1.58	9.47
20	0.787	2.47	14.80
25	0.984	3.85	23.10
30	1.181	5.55	33.30
32	1.260	6.31	37.86
40	1.575	9.86	59.16
50	1.969	15.41	92.46
60	2.362	21.97	131.82
70	2.756	30.22	181.32
80	3.150	39.47	236.82
90	3.543	49.96	299.76
100	3.937	61.65	369.90

• Inch values are approximate metric-to-imperial conversions and do not necessarily represent standard inch stock sizes. Common inch sizes such as 1/4″, 3/8″, 1/2″, 5/8″, 3/4″, 1″, 1-1/2″, and 2″ may be specified separately. For purchasing, always confirm the required standard and nominal size.
• The weights above are theoretical values calculated using a density of 7,850 kg/m³. Actual weight may vary slightly depending on material density and dimensional tolerances.

Common Steel Round Bar Diameter Sizes

Among commonly ordered sizes, 20 mm, 25 mm, 30 mm, 40 mm, 50 mm, and 60 mm steel round bars are frequently used for general fabrication and machining applications.

Larger diameters such as 80 mm, 100 mm, and above are often selected for shafts, heavy machinery components, industrial equipment, and other applications requiring greater cross-sectional area.

The appropriate diameter should be selected according to the required mechanical properties, load conditions, machining dimensions, applicable standard, and end-use requirements rather than diameter alone.

Steel Round Bar Dimensions

The main dimensions used to specify a round bar are diameter and length.

Diameter

Diameter is normally the primary dimension used when ordering a round bar. It determines the cross-sectional area and has a direct effect on the material’s weight.

For example, a 50 mm round bar has a substantially greater weight per meter than a 25 mm round bar because the cross-sectional area increases with the square of the diameter.

Length

Steel round bars can be supplied in standard mill lengths or cut to specific lengths depending on the supplier and application.

Common commercial lengths include:

• 3 m
• 6 m
• 9 m
• 12 m

Cut-to-length service may also be available when customers require specific dimensions for machining or fabrication.

When requesting a quotation, buyers should normally provide the diameter × length, quantity, material grade or standard, and any required surface or machining condition.

Steel Round Bar Weight per Foot

Steel round bar weight per foot is commonly used by buyers working with imperial dimensions or calculating shipping and material requirements.

For a steel round bar, the theoretical weight per foot can be calculated from its diameter and material density. For carbon steel, a commonly used approximate density is 7,850 kg/m³.

The following table provides quick reference values for common inch diameters:

Diameter (in.)	Approx. Weight (lb/ft)
1/4″	0.17
3/8″	0.38
1/2″	0.67
5/8″	1.04
3/4″	1.50
7/8″	2.04
1″	2.67
1-1/4″	4.17
1-1/2″	6.00
1-3/4″	8.17
2″	10.68
2-1/4″	13.52
2-1/2″	16.69
3″	24.04
3-1/2″	32.72
4″	42.74

Weights are theoretical values calculated using a carbon steel density of 7,850 kg/m³. Actual weight may vary depending on material density and dimensional tolerances.

Because weight increases with the square of diameter, even a relatively small increase in diameter can significantly increase the total weight of a round bar.

When purchasing large quantities, calculating weight per foot or per meter helps buyers estimate:

• Total material weight
• Transportation requirements
• Loading capacity
• Shipping costs
• Approximate material cost

For metric purchasing, kg/m is generally more convenient than kg/ft.

How to Calculate Round Bar Weight

The theoretical weight of a steel round bar can be calculated using its diameter, length, and material density.

The basic formula is:

Weight = π × D² ÷ 4 × L × Density

Where:

• D = round bar diameter
• L = round bar length
• Density = material density
• Carbon steel density ≈ 7,850 kg/m³

When using this formula, the diameter and length must be converted into compatible units.

Example: 25 mm Carbon Steel Round Bar

Suppose you have a 25 mm carbon steel round bar with a length of 6 m.

First, calculate the cross-sectional area:

Area = π × 25² ÷ 4 = 490.9 mm²

Using a carbon steel density of 7,850 kg/m³, the theoretical weight is approximately:

3.85 kg/m

For a 6 m bar:

3.85 × 6 ≈ 23.1 kg

Therefore, a 25 mm diameter carbon steel round bar with a 6 m length weighs approximately 23.1 kg per bar.

This is a theoretical calculation. The actual delivered weight can vary slightly because of material density and dimensional tolerances.

Round Bar Weight Calculator Formula

For quick calculations, buyers can use the following simplified formula for carbon steel round bars:

Weight (kg/m) = D² × 0.006165

Where:

• D = diameter in mm
• 0.006165 = approximate coefficient based on a carbon steel density of 7,850 kg/m³

The coefficient is derived from the circular cross-sectional area formula and carbon steel density:

π ÷ 4 × 7,850 ÷ 1,000,000 ≈ 0.006165

Therefore:

Weight (kg/m) = D² × 0.006165

For example, for a 25 mm round bar:

25² × 0.006165 ≈ 3.85 kg/m

For a 6 m bar:

3.85 × 6 ≈ 23.1 kg

This formula provides a convenient way to estimate carbon steel round bar weight without calculating the cross-sectional area separately.

For other materials, the coefficient should be adjusted according to the material’s actual density.

How to Choose the Right Steel Round Bar Size

Selecting a suitable round bar size depends on more than diameter. Buyers should consider the following factors before placing an order.

1. Required Diameter

Select the diameter based on the design drawing, machining allowance, load requirements, and final component dimensions.

If the bar will be machined, the purchased diameter may need to be larger than the finished component size to provide sufficient machining allowance.

2. Required Length

Specify the required standard length or cut length. For large orders, standard mill lengths may reduce cutting waste and simplify transportation.

3. Material Grade and Standard

The required steel grade and standard should be confirmed according to the application and technical specification.

Different standards and grades can have different chemical compositions, mechanical properties, dimensional requirements, and availability.

4. Surface Condition

Round bars may be supplied in different surface conditions, such as hot rolled, cold drawn, peeled, or ground, depending on the required dimensional accuracy and application.

5. Quantity and Total Weight

For commercial purchasing, calculate the approximate total weight from:

Total Weight = Weight per Meter × Length × Quantity

This allows buyers to estimate transportation requirements and compare quotations based on a consistent quantity.

Steel Round Bar Size and Weight: Quick Reference

For quick reference, the most important relationship is:

Larger diameter = higher weight per meter

The weight increases approximately with the square of the diameter. Therefore, doubling the diameter does not simply double the weight.

For example:

• 25 mm round bar ≈ 3.85 kg/m
• 50 mm round bar ≈ 15.41 kg/m
• 100 mm round bar ≈ 61.65 kg/m

A 50 mm bar weighs approximately four times as much per meter as a 25 mm bar, while a 100 mm bar weighs approximately four times as much as a 50 mm bar.

This relationship is particularly important when estimating material costs, lifting requirements, and transportation for larger diameter round bars.

FAQ About Steel Round Bar Sizes and Weight

What are common steel round bar sizes?

Common metric steel round bar sizes include 10, 12, 16, 20, 25, 30, 40, 50, 60, 80, and 100 mm. Common inch sizes include 1/4″, 3/8″, 1/2″, 5/8″, 3/4″, 1″, 1-1/2″, and 2″. Actual availability depends on the applicable standard, grade, and supplier.

How much does a 25 mm steel round bar weigh?

A 25 mm carbon steel round bar weighs approximately 3.85 kg/m, or about 23.1 kg for a 6 m bar.

How do you calculate steel round bar weight?

Use Weight = π × D² ÷ 4 × L × Density. For a quick metric calculation with carbon steel, use Weight (kg/m) = D² × 0.006165.

Does round bar diameter affect weight?

Yes. The theoretical weight of a round bar increases approximately with the square of its diameter, so larger diameter bars become significantly heavier.

What information should I provide when ordering round bar?

Specify the diameter, length, quantity, material grade or standard, surface condition, and any required cutting or machining. This allows the supplier to provide an accurate quotation and confirm availability.

Need Steel Round Bars in Your Required Size?

CJM Steel supplies carbon steel round bars in a range of diameters and lengths for machining, fabrication, machinery, and industrial applications. Custom cutting and required inspection or mill test documentation can be discussed according to your project requirements.

Send us your required diameter × length × grade for a quotation.