Flat bar 12 × 38 in steel — 21.48 kg a piece
Flat bar 12 × 38 weighs 21.48 kg. Its 456 mm² section times a density of 7850 kg/m³ gives 3.58 kg/m, so 100 pieces come to 2147.76 kg and a tonne holds 46.
Only the section formula changes with shape
Plate and flat bar are thickness × width, square bar is side², round bar is π/4 × diameter². Tubes are the outside section minus the inside one: π/4 × (outside² − inside²) for round tube, outside² − inside² for box section, where the inside size is the outside less the wall on both faces, outside − 2t. Subtract the wall only once and you get a tube with half the wall and roughly half the weight — that factor of two is the single most common slip in this calculation.
- t × w456 mm²
- 456 mm² ÷ 10⁶ × 7850 kg/m³3.58 kg/m
- Size
- 12 × 38 mm
- Section formula
- t × w
- Cross-section
- 456 mm²
- Weight per metre
- 3.58 kg/m
- Weight per m²
- 94.2 kg/m²
- Length of one
- 6 m
- Weight of one
- 21.48 kg
- 100 pieces
- 2147.76 kg
- Pieces per tonne
- 46
Nearby cells
Same shape, other sizes
Worth knowing
- Weight per metre (kg/m) is section in mm² ÷ 10⁶ × 7850 — only the section formula changes with shape.
- For plate, thickness × 7.85 is the weight per m²: 47.1 kg/m² at 6 mm, twice that at 12 mm.
- For tube, subtract the inside section from the outside one; the inside size is the outside less 2t.
- Doubling a dimension quadruples the section, while length is directly proportional to weight.
Common questions
Q. How much does one Flat bar 12 × 38 weigh?
21.48 kg — 3.58 kg/m times its length. Ten pieces come to 214.78 kg and a hundred to 2147.76 kg.
Q. How many pieces make a tonne?
46. That is 1000 divided by 21.48 kg, and 100 pieces weigh 2.148 t.
Q. Where does 3.58 kg/m come from?
The section is t × w, which gives 456 mm²; convert that to m² and multiply by a density of 7850 kg/m³. With the dimensions in hand you get the same number without any table.