Hollow sections are sold in 6-meter bars, but project requirements are calculated by weight. With one simple formula you can check the weight of any hollow size — and verify any supplier’s quotation.
The hollow weight formula
For a square/rectangular hollow with sides A × B mm and thickness t mm:
Weight (kg/m) = (A + B − 2t) × 2 × t × 0.00785
The factor 0.00785 is the density of steel (7,850 kg/m³) converted to mm units.
Worked examples
Hollow 40 × 40 × 2 mm:
- (40 + 40 − 4) = 76
- 76 × 2 × 2 = 304 mm²
- 304 × 0.00785 = 2.39 kg/m
- Per 6 m bar: 2.39 × 6 = 14.3 kg
Hollow 50 × 100 × 3 mm:
- (50 + 100 − 6) = 144
- 144 × 2 × 3 = 864 mm²
- 864 × 0.00785 = 6.78 kg/m
- Per 6 m bar: ≈ 40.7 kg
Quick table for popular sizes (per 6 m bar)
| Size (mm) | Thickness (mm) | Weight / 6 m (kg) |
|---|---|---|
| 20 × 40 | 1.5 | ±8.1 |
| 40 × 40 | 1.5 | ±10.9 |
| 40 × 40 | 2 | ±14.3 |
| 40 × 60 | 2 | ±18.1 |
| 50 × 100 | 3 | ±40.7 |
Actual weights may differ slightly due to mill tolerances and corner radii.
Black vs galvanized hollow
The same formula applies to both; galvanized hollow is slightly heavier due to the zinc coating and is typically stocked in 0.7–1.7 mm thicknesses for light applications such as ceilings and partitions. See our hollow size matrix for full availability.
Want us to do the math?
Send us your list of sizes and quantities — the Marselus Steel team will calculate the tonnage and send a quotation the same day.
