Steel Weight Formula:

Weight = Volume × Density

• Volume = size of the steel (m³)

• Density = 7,850 kg/m³

Common Steel Weight Formulas

Plate Formula

Weight (kg) = Length × Width × Thickness × 7,850

Rebar Formula

Weight per metre (kg/m) = D² ÷ 162 Total = kg/m × length × quantity

Steel Density

Density = 7,850 kg/m³

How to calculate steel weight

• Get the dimensions
  From drawings, supplier tables or schedules.

• Convert everything to metres
  Make sure all dimensions are in metres before using the formula.

• Work out the volume
  For plates and flat steel:
  Volume = length × width × thickness

• Multiply by density
  Weight = volume × 7,850

• Convert to tonnes if needed
  Tonnes = kg ÷ 1,000

Example – steel base plate

• Plate size: 400 mm × 400 mm

• Thickness: 20 mm

• Quantity: 4

Convert to metres:

• Length = 0.4 m

• Width = 0.4 m

• Thickness = 0.02 m

Volume per plate:

• 0.4 × 0.4 × 0.02 = 0.0032 m³

Weight per plate:

• 0.0032 × 7,850 = 25.1 kg

Total weight:

• 25.1 × 4 = 100.4 kg (0.10 tonnes)

Follow these steps to calculate weight on site

Common Mistakes

1. Mixing mm and metres
Always keep units consistent before calculating.

2. Using the wrong density
Use 7,850 kg/m³ for standard structural steel.

3. Forgetting quantity
Always multiply by the number of pieces.

4. Wrong bar size (rebar)
Small diameter changes make a big difference (D² rule).

5. No allowance for waste
Allow 5–10% extra for offcuts and site adjustments.

FAQs

Why is steel density 7,850 kg/m³?
It’s the standard average used for structural steel in construction.

When should I use D² / 162?
Use it for rebar only. Use volume × density for plates and sections.

Can I use this formula for all steel types?
Yes, as long as you know the volume or dimensions.

Do I need exact weights?
Estimates are fine for pricing, but accuracy matters for ordering and lifting.