Work out the weight of plate, flat, round, square and tube in seconds. Simple formulas, ready-reference tables and an instant calculator from Heiton Steel.
The basic principle
Weight equals volume times density. Steel has a density of roughly 7,850 kg/m³ (7.85 g/cm³). So for any item:
Weight (kg) = Volume (m³) × 7,850
The formulas below are just this principle rearranged into handy units for each shape, which is why the constants 7.85 and 0.00617 keep appearing.
Steel weight calculator
Results are indicative for mild steel (density 7,850 kg/m³). Final weights are confirmed at quotation.
Formulas by shape
| Shape | Formula | Result |
|---|---|---|
| Plate / sheet | L(m) × W(m) × t(mm) × 7.85 | kg total |
| Flat / rectangular bar | W(mm) × t(mm) × 0.00785 | kg/m |
| Round bar | d(mm)² × 0.00617 | kg/m |
| Square bar | side(mm)² × 0.00785 | kg/m |
| Any shape | cross-section area(m²) × length(m) × 7850 | kg total |
Plate weight reference (kg per m²)
| Thickness (mm) | 3 | 5 | 6 | 8 | 10 | 12 | 20 |
|---|---|---|---|---|---|---|---|
| kg/m² | 23.6 | 39.3 | 47.1 | 62.8 | 78.5 | 94.2 | 157.0 |
Round & square bar reference (kg per m)
| Size (mm) | 10 | 12 | 16 | 20 | 25 | 32 |
|---|---|---|---|---|---|---|
| Round | 0.62 | 0.89 | 1.58 | 2.47 | 3.85 | 6.31 |
| Square | 0.79 | 1.13 | 2.01 | 3.14 | 4.91 | 8.04 |
Worked example
How much does a 6 m length of 100 × 10 mm flat bar weigh?
- Per metre: 100 × 10 × 0.00785 = 7.85 kg/m
- Total: 7.85 × 6 = 47.1 kg
Tip: tube and hollow sections are lighter than solid bar of the same outside size, because the centre is hollow. For those, see our hollow section size guide.
Find the steel you need
Once you know the weight, browse the range and order: Plate, Merchant Bar, Tube, Structural Sections and Reinforcement.
- Tell us the product, size and lengths or quantity.
- Add finishing or cutting where needed.
- We quote competitively and arrange next-working-day delivery with live tracking where available.
Frequently asked questions
What is the density of steel?
Mild steel is about 7,850 kg/m³ (7.85 g/cm³). This is the basis for every steel weight formula.
How do I calculate the weight of a steel plate?
Multiply length (m) × width (m) × thickness (mm) × 7.85. A 2 m × 1 m × 10 mm plate weighs 157 kg.
Why is the round bar constant 0.00617 and not 0.00785?
Because a circle’s area is π/4 (about 0.785) of the square that contains it. Multiplying 0.00785 by π/4 gives roughly 0.00617, the constant for round bar.
Does stainless steel weigh the same as mild steel?
Very close. Stainless is around 7,900-8,000 kg/m³, so it is a little heavier, but the mild steel figures are a good general estimate.