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Unit Weight of Steel

The unit weight of steel is 7,850 kg/m³ (density). In civil engineering it is written as 78.5 kN/m³ (unit weight, IS 875 Part 1). In other units it is 7.85 g/cm³, 7.85 t/m³ and about 490 lb/ft³.

Unit Weight of Steel in Different Units

Unit	Value
kg/m³	7,850
g/cm³	7.85
tonne/m³	7.85
kN/m³	78.5 (as per IS 875 Part 1)
kg/ft³	222.3
lb/ft³	490
lb/in³	0.284

Density of Steel and Other Metals

Material	Density	g/cm³	Unit weight	lb/ft³
Mild steel / TMT	7,850 kg/m³	7.85 g/cm³	77.0 kN/m³	490 lb/ft³
Stainless steel 304	7,930 kg/m³	7.93 g/cm³	77.8 kN/m³	495 lb/ft³
Stainless steel 316	7,980 kg/m³	7.98 g/cm³	78.3 kN/m³	498 lb/ft³
Cast iron	7,200 kg/m³	7.2 g/cm³	70.6 kN/m³	449 lb/ft³
Aluminium	2,700 kg/m³	2.7 g/cm³	26.5 kN/m³	169 lb/ft³
Copper	8,960 kg/m³	8.96 g/cm³	87.9 kN/m³	559 lb/ft³
Brass	8,500 kg/m³	8.5 g/cm³	83.4 kN/m³	531 lb/ft³

Unit weights in kN/m³ here use g = 9.81 m/s². IS 875 (Part 1) lists 78.5 kN/m³ for steel, which designers use for dead load.

Why 7.85 Is Used in Steel Weight Formulas

Because 7,850 kg/m³ equals 7.85 g/cm³, a plate of 1 m × 1 m × 1 mm weighs exactly 7.85 kg. That is why plate weight = length (m) × width (m) × thickness (mm) × 7.85, and section weight = area (mm²) × 0.00785 kg/m.

Unit Weight of TMT Bars (Sariya)

TMT bars use the same density. Weight per meter = D² ÷ 162. See the sariya weight calculator and the rod weight chart.

Frequently Asked Questions

What is the unit weight of steel?

The unit weight (density) of steel is 7,850 kg/m³, or 78.5 kN/m³ as used in IS 875 for structural design.

What is the unit weight of steel in kN/m³?

78.5 kN/m³ as per IS 875 (Part 1). Calculated with g = 9.81, 7,850 kg/m³ is about 77 kN/m³.

What is the density of steel in g/cm³?

7.85 g/cm³ for mild steel. Stainless steel 304 is about 7.93 g/cm³.

What is the unit weight of steel in lb/ft³?

About 490 lb/ft³.

What is the unit weight of steel per cubic foot in kg?

About 222 kg per cubic foot.

Unit Weight of Steel