You are ordering stainless steel bars for a project. The price is quoted per kg, but you only know the size and length. How do you calculate the weight to estimate the cost?

The weight of a stainless steel bar is calculated using the formula: Weight (kg) = Cross-sectional Area (cm²) × Length (m) × Density (g/cm³) ÷ 10¹. For round bars, use: Weight (kg/m) = Diameter² (mm) × 0.00623. For flat bars: Weight (kg/m) = Width (mm) × Thickness (mm) × 0.00793.

I have used these formulas thousands of times for customer quotes. A machine shop needed weight for 20mm round bar. A fabricator needed weight for 50×10mm flat bar. Let me walk you through the calculations.

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How to calculate the weight of a SS bar?

To calculate the weight of a stainless steel bar¹, multiply the cross-sectional area (cm²) by the length (m) and density (g/cm³), then divide by 10. For round bars, use the simplified formula: Weight (kg/m) = Diameter² (mm) × 0.00623 (for 304). For square bars: Weight (kg/m) = Side² (mm) × 0.00793. For flat bars: Weight (kg/m) = Width (mm) × Thickness (mm) × 0.00793.

Example: 20mm round 304 bar weighs 20² × 0.00623 = 2.49 kg per meter.

Weight Formulas by Bar Shape

Let me provide the weight formulas² for different bar shapes.

Round Bar (304/316)

Formula	Example (20mm dia)
Weight (kg/m) = D² (mm) × 0.00623 (304)	20² × 0.00623 = 2.49 kg/m
Weight (kg/m) = D² (mm) × 0.00628 (316)	20² × 0.00628 = 2.51 kg/m

Square Bar (304/316)

Formula	Example (20mm side)
Weight (kg/m) = S² (mm) × 0.00793	20² × 0.00793 = 3.17 kg/m

Flat Bar (304/316)

Formula	Example (50mm × 10mm)
Weight (kg/m) = W (mm) × T (mm) × 0.00793	50 × 10 × 0.00793 = 3.97 kg/m

Hex Bar (304/316)

Formula	Example (20mm across flats)
Weight (kg/m) = AF² (mm) × 0.0072	20² × 0.0072 = 2.88 kg/m

Quick Reference Table (304 Round Bar)

Diameter (mm)	Weight per meter (kg)
6	0.22
8	0.40
10	0.62
12	0.90
16	1.59
20	2.49
25	3.89
32	6.38
40	9.97
50	15.58

My Experience
For a customer ordering 100 meters of 20mm 304 round bar, the total weight was 100 × 2.49 = 249 kg.

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What formula calculates steel bar weight¹?

The general formula for any steel bar weight¹ is: Weight (kg) = Volume (cm³) × Density (g/cm³) ÷ 1000. For a round bar: Weight (kg/m) = π × (D/2)² × 100 × Density ÷ 1000, simplified to D² (mm) × 0.00623 for 304 stainless.

For carbon steel, use 0.00617. For 304 stainless, use 0.00623. For 316 stainless, use 0.00628. The formula works for any diameter in mm.

Formula Constants by Material

Let me provide the simplified formula constants² for different materials.

Round Bar Formula: Weight (kg/m) = D² (mm) × Constant

Material	Constant
Carbon steel (density 7.85)	0.00617
304 stainless (density 7.93)	0.00623
316 stainless (density 8.00)	0.00628
Aluminum (density 2.70)	0.00212
Brass (density 8.50)	0.00668

How the Constant is Derived

Step	Calculation
1	Area (mm²) = π × (D/2)² = π × D²/4
2	Volume (mm³ per m) = Area × 1000
3	Volume (cm³ per m) = Area × 1000 ÷ 1000 = Area
4	Weight (g per m) = Area (mm²) × Density × 0.001?

Actually: Weight (kg/m) = (π × D² × Density) / (4 × 1,000,000)
For 304: π × 7.93 / 4,000,000 = 0.00000623 × D² (mm²) = D² × 0.00623

Example Comparison (50mm round bar)

Material	Constant	Weight per meter (kg)
Carbon steel	0.00617	15.43
304 stainless	0.00623	15.58
316 stainless	0.00628	15.70

My Experience
For a mixed order of carbon steel and stainless bars, I use different constants: 0.00617 for carbon, 0.00623 for 304, 0.00628 for 316.

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How to calculate the bar weight¹?

To calculate bar weight¹, follow these steps: 1) Measure the diameter or dimensions accurately. 2) Calculate the cross-sectional area². 3) Multiply area by length to get volume. 4) Multiply volume by density. For round bars, use the simplified formula directly.

Example: A 304 round bar, 25mm diameter, 6m length. Weight = 25² × 0.00623 × 6 = 625 × 0.00623 × 6 = 23.36 kg.

Step-by-Step Calculation Examples

Let me provide detailed examples for different bar shapes.

Example 1: Round Bar (304, 30mm dia, 4m length)

Step	Calculation	Result
1	D²	30² = 900
2	× constant	900 × 0.00623 = 5.607 kg/m
3	× length	5.607 × 4 = 22.43 kg

Example 2: Flat Bar (316, 60mm × 12mm, 5m length)

Step	Calculation	Result
1	Area (mm²)	60 × 12 = 720
2	× density factor	For 316 flat bar: W × T × 0.0080
3	Weight per meter	60 × 12 × 0.0080 = 5.76 kg/m
4	× length	5.76 × 5 = 28.8 kg

Example 3: Square Bar (304, 40mm side, 3m length)

Step	Calculation	Result
1	S²	40² = 1,600
2	× constant (0.00793)	1,600 × 0.00793 = 12.69 kg/m
3	× length	12.69 × 3 = 38.07 kg

Common Mistakes to Avoid

• Using the wrong constant for the material
• Forgetting to convert units (mm to m)
• Using diameter instead of radius in area formula
• Mixing metric and imperial units

My Experience
A customer calculated the weight of a 20mm bar using the carbon steel constant and underquoted their shipping. I corrected it to 0.00623 for 304.

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How is SS 304 sheet weight¹ calculated?

SS 304 sheet weight¹ is calculated using the formula: Weight (kg) = Length (m) × Width (m) × Thickness (mm) × 7.93. For a 1m × 2m × 2mm sheet, weight = 1 × 2 × 2 × 7.93 = 31.72 kg.

For quick estimation, use 8.0 instead of 7.93. For imperial (4×8 sheet), use: Weight (lb) = Length (ft) × Width (ft) × Thickness (in) × 40.8. A 4×8 × 1/8 in sheet weighs 4 × 8 × 0.125 × 40.8 = 163 lb.

Sheet Weight Formulas

Let me provide the formulas for stainless steel sheet weight.

Metric Formula

Formula	Example (1m × 2m × 2mm)
Weight (kg) = L(m) × W(m) × T(mm) × 7.93	1 × 2 × 2 × 7.93 = 31.72 kg

Quick Estimation (Using 8.0)

Formula	Example (1m × 2m × 2mm)
Weight (kg) = L × W × T × 8.0	1 × 2 × 2 × 8.0 = 32 kg

Imperial Formula

Formula	Example (4ft × 8ft × 1/8 in)
Weight (lb) = L(ft) × W(ft) × T(in) × 40.8	4 × 8 × 0.125 × 40.8 = 163 lb

Weight per Square Meter (304)²

Thickness (mm)	Weight per m² (kg)
0.5	3.97
1.0	7.93
1.5	11.90
2.0	15.86
2.5	19.83
3.0	23.79
4.0	31.72
5.0	39.65
6.0	47.58

Comparison: 304 vs 316 Sheet Weight (2mm thick, 1m²)

Grade	Density (g/cm³)	Weight per m² (kg)
304	7.93	15.86
316	8.00	16.00
Carbon steel	7.85	15.70

My Experience
For a customer ordering 50 sheets of 1m × 2m × 2mm 304, total weight = 50 × 31.72 = 1,586 kg. They used this for freight calculation.

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Conclusion

304 stainless steel bar weight¹ (kg/m) = D² × 0.00623 for round bars, W × T × 0.00793 for flat bars. 304 sheet weight² (kg) = L × W × T × 7.93 (metric) or L × W × T × 8.0 for quick estimate.

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