How to Calculate Weight of Steel — The Definitive Formula Guide for Every Section Type

If you work with steel in any capacity — trading, procurement, fabrication, construction, or engineering — calculating weight is something you do repeatedly. Every purchase order, every delivery verification, every project estimate, every BOQ depends on getting the weight right.

This guide covers the weight formula for every common steel section type, with fully worked examples using real-world dimensions. Every formula has been verified against IS standard density values and cross-checked with industry references. Use this as your permanent reference, or use our free Steel Weight Calculator for instant results.

The One Principle Behind All Steel Weight Calculations

Every steel weight calculation follows one principle:

Weight = Volume × Density

That’s it. Whether you’re calculating the weight of a TMT bar, a 40mm plate, a 6-inch pipe, or an ISMB 300 beam, you’re always doing the same thing — calculating the volume of the steel shape and multiplying it by the density of the specific material.

The reason different section types have different formulas is simply that they have different shapes. A round bar has a circular cross-section. A plate is rectangular. A pipe is a hollow cylinder. An angle is an L-shape. The volume calculation changes with the shape, but the principle never does.

The density of mild steel — the number that converts volume into weight — is 7,850 kg/m³. This is the standard value used globally for carbon steel and structural steel (IS 2062, ASTM A36, EN S275JR). When you see constants like 162, 7.85, or 0.00785 in steel weight formulas, they all derive from this single density value.

Steel Density: The Number You Need to Know

The density of mild steel is 7,850 kg per cubic metre. This can also be expressed as 7.85 grams per cubic centimetre, 78.5 kilonewtons per cubic metre, or 490 pounds per cubic foot.

Different steel alloys and metals have different densities:

• Mild Steel / Carbon Steel (IS 2062, Fe 500D): 7,850 kg/m³
• Stainless Steel 304: 8,000 kg/m³
• Stainless Steel 316: 8,027 kg/m³
• Stainless Steel 202: 7,860 kg/m³
• Galvanised Steel: 7,850 kg/m³ (zinc coating adds negligible density change)
• Aluminium 6061: 2,700 kg/m³
• Copper: 8,940 kg/m³
• Brass: 8,500 kg/m³
• Cast Iron (Grey): 7,200 kg/m³
• Titanium Grade 2: 4,510 kg/m³

All formulas in this guide assume mild steel at 7,850 kg/m³ unless stated otherwise. To calculate weight for other materials, use the Metal Weight Calculator or apply the correction factor explained in the materials section below.

TMT Bar / Round Bar — d²/162 Formula

The formula: Weight (kg per metre) = d² ÷ 162

Where d is the diameter of the bar in millimetres. This gives weight in kg per metre of length.

Where 162 comes from: The full formula is (π/4) × d² × 7850 / 10⁶. When you work through the algebra: 4 × 10⁶ ÷ (π × 7850) = 162.20. The industry standard rounds this to 162 for practical use. The difference between 162 and 162.2 is less than 0.12%, which is well within manufacturing tolerances.

Quick reference — all standard TMT sizes:

6mm: 0.222 kg/m. 8mm: 0.395 kg/m. 10mm: 0.617 kg/m. 12mm: 0.889 kg/m. 16mm: 1.580 kg/m. 20mm: 2.469 kg/m. 25mm: 3.858 kg/m. 28mm: 4.840 kg/m. 32mm: 6.321 kg/m. 36mm: 8.000 kg/m. 40mm: 9.877 kg/m.

For instant calculations with any diameter, length, and quantity, use the TMT Bar Weight Calculator. For the complete chart, see our TMT Bar Weight Per Metre Chart.

Steel Plate / Sheet — Thickness × 7.85 Formula

The formula: Weight (kg per square metre) = thickness (mm) × 7.85

This gives weight per square metre. For a specific plate size, multiply by the area in square metres.

The full formula: Weight (kg) = length (mm) × width (mm) × thickness (mm) × 7.85 ÷ 1,000,000

Where 7.85 comes from: The density 7,850 kg/m³ divided by 1,000 (to convert from per-cubic-metre to per-millimetre-of-thickness per-square-metre) equals 7.85.

Quick reference — common plate thicknesses:

1mm: 7.85 kg/m². 2mm: 15.70 kg/m². 3mm: 23.55 kg/m². 5mm: 39.25 kg/m². 6mm: 47.10 kg/m². 8mm: 62.80 kg/m². 10mm: 78.50 kg/m². 12mm: 94.20 kg/m². 16mm: 125.60 kg/m². 20mm: 157.00 kg/m². 25mm: 196.25 kg/m². 32mm: 251.20 kg/m². 40mm: 314.00 kg/m². 50mm: 392.50 kg/m².

The pattern is simple: every 1mm of thickness adds 7.85 kg per square metre. Once you memorise “10mm = 78.5 kg/m²,” you can mentally estimate any plate weight.

For detailed calculations, use the Steel Plate Weight Calculator. For the complete chart, see our Steel Plate Weight Chart.

MS Pipe — (OD − WT) × WT × 0.02466 Formula

The formula: Weight (kg per metre) = (OD − WT) × WT × 0.02466

Where OD is the outer diameter in mm and WT is the wall thickness in mm.

Where 0.02466 comes from: The cross-sectional area of a thin-walled pipe is approximately π × (OD − WT) × WT. Multiply by the density: π × 7850 / 10⁶ = 0.024662, which rounds to 0.02466.

Important note: Pipes in India are specified by Nominal Bore (NB), not by outer diameter. A “50mm NB pipe” has an OD of 60.3mm, not 50mm. Always verify the OD and WT from the IS 1239 standard tables before calculating.

Quick reference — standard MS pipe weights (IS 1239 medium class):

15mm NB (½”): OD 21.3, WT 2.6 → 1.20 kg/m. 20mm NB (¾”): OD 26.9, WT 2.6 → 1.56 kg/m. 25mm NB (1”): OD 33.7, WT 3.2 → 2.41 kg/m. 32mm NB (1¼”): OD 42.4, WT 3.2 → 3.10 kg/m. 40mm NB (1½”): OD 48.3, WT 3.2 → 3.56 kg/m. 50mm NB (2”): OD 60.3, WT 3.6 → 5.03 kg/m. 80mm NB (3”): OD 88.9, WT 4.0 → 8.38 kg/m. 100mm NB (4”): OD 114.3, WT 4.5 → 12.18 kg/m. 150mm NB (6”): OD 168.3, WT 5.0 → 20.14 kg/m. 200mm NB (8”): OD 219.1, WT 6.3 → 33.05 kg/m.

Note: These are medium (Class B) weights. Light class (Class A) pipes have thinner walls and weigh less. Heavy class (Class C) pipes have thicker walls and weigh more.

For instant pipe weight calculations, use the MS Pipe Weight Calculator. For the full chart, see our MS Pipe Weight Chart.

Steel Angle — (A + B − T) × T × 0.00785 Formula

The formula: Weight (kg per metre) = (A + B − T) × T × 0.00785

Where A and B are the leg lengths in mm, and T is the thickness in mm. For equal angles, A = B.

Where 0.00785 comes from: This is simply 7850 / 1,000,000 = 0.00785. It converts the cross-section area (in mm²) directly to weight per metre (in kg/m).

Important caveat: This formula is a simplified approximation that assumes sharp corners. Real rolled angles have root radius and toe radius as specified in IS 808. For smaller angles (up to 65×65mm), the formula is accurate within 1–2%. For larger angles (75mm and above), the root radius becomes significant and the formula may differ from IS 808 published values by 1–3%. For large angles, use the IS 808 published weights available in our Steel Angle Weight Calculator.

Quick reference — common equal angle weights:

25×25×3: 1.11 kg/m. 25×25×5: 1.77 kg/m. 40×40×5: 2.95 kg/m. 40×40×6: 3.48 kg/m. 50×50×5: 3.73 kg/m. 50×50×6: 4.43 kg/m. 65×65×6: 5.84 kg/m. 75×75×6: 6.77 kg/m. 75×75×8: 8.90 kg/m. 100×100×8: 11.98 kg/m (IS 808). 100×100×10: 14.73 kg/m (IS 808). 150×150×12: 26.87 kg/m (IS 808).

Flat Bar — Width × Thickness × 0.00785 Formula

The formula: Weight (kg per metre) = Width (mm) × Thickness (mm) × 0.00785

This is the simplest formula because a flat bar has a rectangular cross-section — just width times thickness.

Useful mental check: A 100mm wide, 10mm thick flat bar weighs exactly 7.85 kg/m — directly reflecting the density of steel (7.85 g/cm³). Memorise this: 100×10 = 7.85.

For instant calculations, use the Flat Bar Weight Calculator.

Square Tube — 4 × (Side − WT) × WT × 0.00785 Formula

The formula: Weight (kg per metre) = 4 × (Side − WT) × WT × 0.00785

Where Side is the outer dimension in mm and WT is the wall thickness in mm. The factor 4 accounts for the four walls of the square cross-section.

For all sizes, use the Square Tube Weight Calculator.

Rectangular Tube — 2 × (W + H − 2WT) × WT × 0.00785 Formula

The formula: Weight (kg per metre) = 2 × (Width + Height − 2 × WT) × WT × 0.00785

Where Width and Height are the outer dimensions in mm and WT is the wall thickness in mm.

For instant calculations, use the Rectangular Tube Weight Calculator.

I-Beam (ISMB) and Channel (ISMC) — IS 808 Standard Lookup

I-beams and channels have complex cross-sectional profiles with flanges, webs, and fillets (root radius). Calculating their weight from first principles requires knowing the exact profile dimensions including the fillet radius — which is impractical for everyday use.

Instead, use the IS 808 published standard weight per metre. These values are calculated from the actual rolled section geometry and account for all radii and tapers.

ISMB (Indian Standard Medium Weight Beam) — common sizes:

ISMB 100: 11.5 kg/m. ISMB 150: 14.9 kg/m. ISMB 200: 25.4 kg/m. ISMB 250: 37.3 kg/m. ISMB 300: 46.1 kg/m. ISMB 350: 52.4 kg/m. ISMB 400: 61.6 kg/m. ISMB 450: 72.4 kg/m. ISMB 500: 86.9 kg/m. ISMB 600: 122.6 kg/m.

ISMC (Indian Standard Medium Weight Channel) — common sizes:

ISMC 75: 6.8 kg/m. ISMC 100: 9.2 kg/m. ISMC 125: 12.7 kg/m. ISMC 150: 16.4 kg/m. ISMC 200: 22.1 kg/m. ISMC 250: 30.4 kg/m. ISMC 300: 36.3 kg/m. ISMC 400: 49.4 kg/m.

For the complete database with section properties (moment of inertia, section modulus), use the I-Beam Weight Calculator and Channel Weight Calculator.

Chequered Plate — Base Weight + 5% Pattern Allowance

The formula: Weight (kg per m²) = thickness (mm) × 7.85 × 1.05

Chequered (checker) plates have a raised diamond pattern on one surface. The 5% addition accounts for the extra metal in this pattern.

Important note: The 5% is an industry standard approximation. Actual pattern weight varies between 4.5–5.5% depending on the manufacturer. Enter the base plate thickness (excluding the pattern height), and the 5% is added automatically.

How to Adjust for Different Materials

All formulas above assume mild steel at 7,850 kg/m³. For other materials, multiply the mild steel result by a correction factor:

• Stainless Steel 304 (8,000 kg/m³): multiply by 1.019
• Stainless Steel 316 (8,027 kg/m³): multiply by 1.023
• Stainless Steel 202 (7,860 kg/m³): multiply by 1.001 (negligible difference)
• Aluminium 6061 (2,700 kg/m³): multiply by 0.344
• Copper (8,940 kg/m³): multiply by 1.139
• Brass (8,500 kg/m³): multiply by 1.083
• Cast Iron Grey (7,200 kg/m³): multiply by 0.917
• Titanium Grade 2 (4,510 kg/m³): multiply by 0.574

For multi-material calculations, use the Metal Weight Calculator which supports 19 materials.

Quick Reference: The 20 Most Common Steel Weights

These are the weights that steel professionals look up most frequently. Memorising even a few of these saves significant time.

Where the Constants Come From — Formula Derivations

Understanding where the constants come from helps you verify formulas and adapt them for non-standard situations.

The constant 162 (TMT/Round bar):

The constant 7.85 (Plate/Sheet):

The constant 0.02466 (Pipe):

The constant 0.00785 (Angle, Flat bar, Tube):

Common Mistakes and How to Avoid Them

Mistake 1: Confusing NB with OD for pipes. A “50mm pipe” in India means 50mm Nominal Bore, which has an OD of 60.3mm. Using 50 as the OD in the formula gives a completely wrong result. Always look up the actual OD and WT from IS 1239 tables.

Mistake 2: Forgetting to account for gauge thickness. Sheet metal is often specified by gauge number (18 gauge, 20 gauge) rather than mm. 18 gauge is 1.214mm (MSG), not 18mm. Use a Gauge to MM Converter to get the actual thickness before calculating.

Mistake 3: Using the wrong density for stainless steel. SS 304 is 8,000 kg/m³, not 7,850. A 10mm SS 304 plate weighs 80.0 kg/m², not 78.5. The 2% difference adds up on large orders.

Mistake 4: Not accounting for chequered plate pattern. A 10mm chequered plate weighs 82.4 kg/m², not 78.5. The 5% pattern allowance is easy to forget when estimating.

Mistake 5: Using the simplified angle formula for large sections. The formula (A + B − T) × T × 0.00785 underestimates weight for angles 75mm and above because it ignores root radius. Use IS 808 published values for large angles.

Mistake 6: Confusing weight per metre with weight per piece. Always multiply weight per metre by the actual length to get piece weight. A standard TMT bar is 12m, a standard pipe is 6m, and a standard angle is 6m — but non-standard lengths are common.

Frequently Asked Questions

What is the formula to calculate weight of steel?

The universal formula is Weight = Volume × Density. For mild steel, density is 7,850 kg/m³. Simplified formulas for each section type: TMT bar: d² ÷ 162 × length. Plate: length(mm) × width(mm) × thickness(mm) × 7.85 / 1,000,000. Pipe: (OD − WT) × WT × 0.02466 × length. Angle: (A + B − T) × T × 0.00785 × length. All dimensions in mm, lengths in metres, results in kg.

What is the unit weight of steel?

The unit weight (density) of mild steel is 7,850 kg per cubic metre. This equals 7.85 g/cm³, 78.5 kN/m³, or 490 lb/ft³. For stainless steel 304, it is 8,000 kg/m³. For aluminium, it is 2,700 kg/m³.

How much does a 12mm TMT bar weigh per metre?

A 12mm TMT bar weighs 0.889 kg per metre. Calculation: 12² ÷ 162 = 144 ÷ 162 = 0.889 kg/m. A standard 12m bar weighs 10.67 kg. Approximately 93 bars make one tonne.

What is the weight of a 10mm MS plate per square metre?

A 10mm MS plate weighs 78.5 kg per square metre. The formula is simply: thickness in mm × 7.85 = kg/m². A standard 1500×6000mm plate at 10mm weighs 706.5 kg.

How do you calculate MS pipe weight?

Use the formula: Weight (kg/m) = (OD − Wall Thickness) × Wall Thickness × 0.02466. All dimensions in mm. For a 50mm NB pipe (OD 60.3mm, WT 3.6mm): (60.3 − 3.6) × 3.6 × 0.02466 = 5.03 kg/m. Always use OD, not NB, in the formula.

What is the constant 162 in the steel weight formula?

The constant 162 (precisely 162.2) is derived from: 4 × 10⁶ ÷ (π × 7850) = 162.20. It simplifies the expression (π/4) × d² × 7850 / 10⁶ into the quick formula d²/162. Some references use 162, others 162.2 — the difference is less than 0.12%.

How to calculate weight of steel angle?

For equal angles: Weight (kg/m) = (Leg A + Leg B − Thickness) × Thickness × 0.00785. For a 50×50×5mm angle: (50 + 50 − 5) × 5 × 0.00785 = 3.73 kg/m. For angles 75mm and larger, use IS 808 published standard weights for better accuracy, as the simplified formula doesn’t account for root radius.

All formulas in this guide use mild steel density of 7,850 kg/m³ unless stated otherwise. Values are calculated to 2–3 decimal places. Minor variations (typically under 1%) may exist compared to other references due to rounding differences in the density constant. IS 808 standard values are used for I-beams, channels, and large angles. For instant calculations, use SteelMath’s free Steel Weight Calculator.

Related on SteelMath: Steel Weight Calculator — Complete Guide · TMT Bar Weight Per Metre Chart · Steel Plate Weight Chart · MS Pipe Weight Chart · Steel Angle Weight Chart · Steel Weight Calculator