How to Calculate Steel Weight: Formulas for Every Shape

To calculate steel weight, find the volume of the piece and multiply by the density of steel, 7,850 kg/m³. In practice you use a short formula for each shape: for example, a plate weighs thickness (mm) × 7.85 kg per square metre, and a round bar weighs diameter² ÷ 162 kg per metre.

Key takeaways

• Every formula below is volume × 7,850 kg/m³, simplified for millimetre sizes.
• Results are theoretical; rolled steel is billed on weighbridge weight.
• For standard beams and channels, use the published IS 808 tables instead of formulas.
• Our steel weight calculator does these sums for you.

Which formula should I use for each shape?

All sizes are in millimetres unless stated; results are in kilograms.

Shape	Formula	Example	Result
Plate / sheet	L (m) × W (m) × t (mm) × 7.85	2.5 m × 1.25 m × 10 mm	245.3 kg
Flat bar	W × t × 0.00785 per metre	50 × 6 mm	2.36 kg/m
Round bar / TMT	d² ÷ 162 per metre	20 mm	2.47 kg/m
Square bar / billet	a² × 0.00785 per metre	100 × 100 mm	78.5 kg/m
Hexagon bar	s² × 0.0068 per metre (s = across flats)	30 mm	6.12 kg/m
Pipe / round tube	(OD − t) × t × 0.02466 per metre	48.3 OD × 3.2 mm	3.56 kg/m
Equal angle	(2a − t) × t × 0.00785 per metre	50 × 50 × 6 mm	4.43 kg/m
Square hollow section	4 × (a − t) × t × 0.00785 per metre	40 × 40 × 2.5 mm	2.94 kg/m

The angle and hollow-section formulas ignore the rounded root or corners, so actual rolled weight is usually 1–2% different.

How do you calculate MS plate weight?

Multiply the area in square metres by the thickness in millimetres and by 7.85. The 7.85 is simply steel density written as kg per square metre per millimetre of thickness.

Example: a standard 2,500 × 1,250 mm plate, 12 mm thick. 2.5 × 1.25 × 12 × 7.85 = 294.4 kg.

If you work in feet, a quick rule is thickness (mm) × 0.729 kg per square foot. See standard thicknesses on our MS plates page.

How do you calculate MS flat weight?

Weight per metre = width × thickness × 0.00785. Multiply by the length in metres for one piece.

Example: 75 × 10 mm flat, 6 m long. 75 × 10 × 0.00785 = 5.89 kg/m, so one 6 m length ≈ 35.3 kg.

A ready table of common sizes is on the MS flats page.

How do you calculate round bar and TMT weight?

Use d² ÷ 162 kg per metre, where d is the diameter in millimetres. The 162 comes from π ÷ 4 × 7,850 ÷ 1,000,000, inverted.

Example: 16 mm bar, 12 m long. 16² ÷ 162 = 1.58 kg/m, so one bar ≈ 19 kg. Our TMT weight chart lists every diameter with bars per tonne.

How do you calculate pipe weight?

For a round pipe, weight per metre = (OD − t) × t × 0.02466, where OD is the outside diameter and t the wall thickness, both in mm.

Example: 88.9 mm OD pipe with 4 mm wall. (88.9 − 4) × 4 × 0.02466 = 8.37 kg/m.

Pipes sold to IS 1239 or IS 3589 also have published weight tables, which should be your reference for billing. See our steel pipes page.

Why not use a formula for beams and channels?

Beams (ISMB) and channels (ISMC) have tapered flanges and root radii, so a simple formula is not accurate. Use the sectional weights published in IS 808 instead. The MS beams page and MS channels page list the common sizes.

How do you turn weight into an order quantity?

1. Calculate the weight of each item with the formulas above.
2. Multiply by the number of pieces.
3. Add an allowance for cutting wastage (often 2–5%, depending on cut lengths).
4. Total everything and divide by 1,000 to get metric tonnes (MT).

Steel is quoted per MT, so this total is what you compare between suppliers. Check whether each quote includes GST, loading and freight.

How RLG Ispat can help

RLG Ispat supplies plates, flats, rounds, TMT, pipes, angles, beams and channels from Raipur with GST billing and MTC/TC support where applicable. Send your size-wise list through the quote form or WhatsApp +91 75870 51838, and our sales desk will check the weights with you and confirm rate and dispatch.