Steel Weight Calculator — The Complete Guide With Formulas for Every Section

Whether you’re preparing a purchase order, estimating a project, or verifying a supplier’s invoice, knowing how to calculate steel weight accurately is one of the most essential skills in the steel industry. This guide covers every common steel section with formulas, worked examples, and access to our free online calculator that does the maths instantly.

The Universal Principle

All steel weight calculations follow one principle: Weight = Volume × Density. The density of mild steel (carbon steel) is 7,850 kg per cubic metre. For stainless steel 304, it’s 8,000 kg/m³. For aluminium, 2,700 kg/m³.

The challenge is calculating the volume correctly for each section shape. That’s what the formulas below solve.

TMT Bar / Round Bar

This is the most commonly calculated section in Indian construction and trading.

The simplified formula is: Weight (kg) = d² ÷ 162.2 × Length (m)

Where d is the diameter in millimetres and 162.2 is a constant derived from the density of mild steel and the area formula for a circle.

Example: A 12mm TMT bar, 12 metres long. Weight = 12² ÷ 162.2 × 12 = 144 ÷ 162.2 × 12 = 10.66 kg per bar.

For 100 such bars: 10.66 × 100 = 1,066 kg = 1.066 MT.

Quick reference for common TMT bar weights per metre: 8mm weighs 0.395 kg/m, 10mm weighs 0.617 kg/m, 12mm weighs 0.889 kg/m, 16mm weighs 1.580 kg/m, 20mm weighs 2.469 kg/m, 25mm weighs 3.853 kg/m, and 32mm weighs 6.313 kg/m.

Steel Plate / Sheet

Formula: Weight (kg) = Length (mm) × Width (mm) × Thickness (mm) × 7.85 ÷ 1,000,000

The constant 7.85 comes from converting the density of mild steel (7,850 kg/m³) into a form usable with millimetre dimensions.

Example: A plate measuring 2,000mm × 1,000mm × 10mm thick. Weight = 2000 × 1000 × 10 × 7.85 ÷ 1,000,000 = 157 kg.

For chequered (checker) plates, add approximately 5% to the calculated weight to account for the raised diamond pattern.

MS Pipe / Round Tube

Formula: Weight (kg/m) = (OD − Wall Thickness) × Wall Thickness × 0.02466

Where OD is the outer diameter in mm and Wall Thickness is in mm. The constant 0.02466 is derived from π × density ÷ 10⁶.

Example: A pipe with 60mm OD and 3.6mm wall thickness. Weight per metre = (60 − 3.6) × 3.6 × 0.02466 = 56.4 × 3.6 × 0.02466 = 5.01 kg/m.

For a 6-metre length: 5.01 × 6 = 30.06 kg.

Square Tube

Formula: Weight (kg/m) = (Side − Wall Thickness) × Wall Thickness × 4 × 0.00785

Example: A 50mm × 50mm square tube with 2.5mm wall thickness. Weight per metre = (50 − 2.5) × 2.5 × 4 × 0.00785 = 47.5 × 2.5 × 4 × 0.00785 = 3.73 kg/m.

Rectangular Tube

Formula: Weight (kg/m) = 2 × (Width + Height − 2 × Wall Thickness) × Wall Thickness × 0.00785

Example: A 75mm × 50mm rect tube with 3mm wall. Weight per metre = 2 × (75 + 50 − 6) × 3 × 0.00785 = 2 × 119 × 3 × 0.00785 = 5.61 kg/m.

Angle Section

Formula: Weight (kg/m) = (Leg A + Leg B − Thickness) × Thickness × 0.00785

Example: A 50mm × 50mm × 5mm angle. Weight per metre = (50 + 50 − 5) × 5 × 0.00785 = 95 × 5 × 0.00785 = 3.73 kg/m.

Flat Bar

Formula: Weight (kg/m) = Width (mm) × Thickness (mm) × 0.00785

Example: A 50mm × 6mm flat bar. Weight per metre = 50 × 6 × 0.00785 = 2.355 kg/m.

I-Beam and Channel

For standard I-beams (ISMB) and channels (ISMC), weights are defined by Indian Standard specifications. These sections have complex cross-sectional profiles (flanges, web, fillets) that make direct formula calculation impractical. Instead, use the IS standard lookup tables.

Common ISMB weights per metre: ISMB 100 is 11.5 kg/m, ISMB 150 is 14.9 kg/m, ISMB 200 is 25.4 kg/m, ISMB 250 is 37.3 kg/m, ISMB 300 is 46.1 kg/m, ISMB 350 is 52.4 kg/m, and ISMB 400 is 61.6 kg/m.

Our Steel Weight Calculator has the complete IS standard database built in — just select the section size and the weight is auto-filled.

Adjusting for Different Materials

All formulas above assume mild steel (7,850 kg/m³). For other materials, multiply the result by a correction factor: Stainless Steel 304 uses factor 1.019, Stainless Steel 316 uses 1.023, Aluminium uses 0.344, Copper uses 1.139, and Brass uses 1.083.

Or simply use our calculator and select the material from the dropdown — the density is automatically applied.

Use the Free Calculator

Rather than calculating manually every time, use SteelMath’s Steel Weight Calculator. It supports all 10 section types, all materials, calculates instantly as you type, and lets you build multi-item BOMs (Bills of Materials) with one-click export to PDF or WhatsApp.

It’s free, requires no signup, and works on mobile. Try it now.