Hong Life CalculatorsUnderstanding the steel weight calculator — concept and principle
This calculator gives the weight of a steel plate or flat bar, a round bar, a round pipe or a square tube from its dimensions and the material density. It is used to estimate shipping and lifting loads, order material priced by the kilogram, or check the dead load a frame adds to a structure. Changing the density lets you use it for aluminium or stainless steel.
How it is calculated
Weight = volume × density (kg/m³). Lengths in mm are divided by 1,000 to get metres.
- Plate / flat bar: V = L × W × t.
- Round bar: V = π × (Ø/2)² × L.
- Pipe: V = π × [(OD/2)² − (ID/2)²] × L, with ID = OD − 2 × wall.
- Square tube: V = [side² − (side − 2 × wall)²] × L.
Per metre of length is weight ÷ L for every shape; for bars and hollow sections it is the usual catalogue figure, and for a plate it applies at the entered width.
The principle
Density is mass per unit volume, so any solid's mass is its volume times its density. For prismatic shapes the volume is simply the cross-section area times the length. Hollow sections are the outer area minus the inner hole. Carbon steel is about 7,850 kg/m³, stainless steel about 7,900–8,000 kg/m³ and aluminium about 2,700 kg/m³. The square-tube formula assumes sharp corners; real tubes have rounded corners and weigh slightly less than calculated.
Worked example
- Inputs: plate shape, L = 6 m, width 60 mm, thickness 4 mm, density 7,850 kg/m³.
- Convert to metres: 0.060 m × 0.004 m.
- Volume: 6 × 0.060 × 0.004 = 0.00144 m³.
- Weight: 0.00144 × 7,850 = 11.304, shown as 11.3 kg.
- Per metre of length: 11.304 ÷ 6 = 1.88 kg/m.
| Length L (m) | Weight (kg) |
|---|---|
| 1.5 | 2.83 |
| 3 | 5.65 |
| 4.5 | 8.48 |
| 6 | 11.3 |
| 7.5 | 14.13 |
| 9 | 16.96 |
| 12 | 22.61 |
How to read the result
Compare shapes of the same outer size: a 60 mm round pipe with a 4 mm wall and 6 m length weighs about 33.1 kg, a 60 mm square tube with the same wall about 42.2 kg, and a 60 mm solid round bar about 133 kg. Hollow sections give much more stiffness per kilogram. For orders, add an allowance for cutting waste, and use the supplier's tables when tolerances matter, since actual thickness can vary.
Common mistakes
- Mixing mm and m: the length field is in metres while the cross-section is in mm.
- Using the inside diameter as OD for pipe; nominal pipe sizes are not the actual outside diameter.
- Forgetting to change density for aluminium or stainless steel.
Frequently asked questions
How heavy is a 1 m² steel plate 1 mm thick?
About 7.85 kg, since 1 m² × 0.001 m × 7,850 kg/m³ = 7.85 kg.
Why is stainless heavier than mild steel?
Its alloying elements, mainly chromium and nickel, give it a slightly higher density.
Does galvanising add weight?
Yes, the zinc coating adds a small amount, which matters mainly for thin sheet and large quantities.
Sources: EN 1991-1-1 (Eurocode 1), Annex A, nominal densities of construction materials · CRC Handbook of Chemistry and Physics