Steel is drawn in rods, ordered in tonnes and priced in kilograms. Converting between the three is the most common calculation on a building site, and the one where small mistakes become large bills. This chart and the formula behind it are all you need.
TMT Bar Weight Chart (IS 1786)
Bars in India are rolled in standard 12 metre lengths. The nominal mass per metre is set by IS 1786.
| Diameter | kg per metre | kg per 12 m rod | Rods per tonne | Price page |
|---|---|---|---|---|
| 8 mm | 0.395 | 4.74 | 211 | 8mm price |
| 10 mm | 0.617 | 7.40 | 135 | 10mm price |
| 12 mm | 0.888 | 10.66 | 94 | 12mm price |
| 16 mm | 1.58 | 18.96 | 53 | 16mm price |
| 20 mm | 2.47 | 29.64 | 34 | 20mm price |
| 25 mm | 3.85 | 46.20 | 22 | 25mm price |
| 32 mm | 6.31 | 75.72 | 13 | 32mm price |
Rod counts per tonne are rounded; actual counts vary by a rod or so because of rolling tolerance.
Where Does the D²/162 Formula Come From?
Steel has a density of about 7,850 kg per cubic metre. A bar of diameter D millimetres and 1 metre length has a volume of π × (D/2)² mm² × 1,000 mm. Converting units and multiplying by density gives:
Weight (kg/m) = D² × π / 4 × 7,850 / 1,000,000 ≈ D² / 162.2
Site engineers round it to D² ÷ 162. For a 16 mm bar: 16 × 16 ÷ 162 = 1.58 kg per metre, exactly the IS 1786 figure. For quick mental arithmetic it is the only formula you need.
How Do You Convert Rods to Tonnes, and Back?
Rods to weight: number of rods × 12 m × kg per metre. For example, 150 rods of 10 mm = 150 × 12 × 0.617 = 1,110.6 kg, or about 1.11 tonnes.
Tonnes to rods: 1,000 ÷ (12 × kg per metre) per tonne. For example, 2 tonnes of 16 mm = 2 × 1,000 ÷ 18.96 = about 105 rods.
Price per rod: price per kg × kg per rod. At ₹55 a kg, a 12 mm rod costs 55 × 10.66 = about ₹586.
Why Should You Weigh Bars on Delivery?
A bar's strength depends on its cross-sectional area, and the engineer's design assumes the full nominal size. A bar that is underweight is thinner than its label, and in the worst cases of substandard steel, rods marked 12 mm weigh what a 11 mm bar should. You cannot see a millimetre with your eye; you can weigh it.
To check a delivery:
- Pick three or four rods at random from different bundles.
- Weigh each, or measure the length and weigh a cut piece.
- Compare with the chart. A 12 m rod of 12 mm should weigh about 10.66 kg.
- A small variation within IS 1786 tolerance is normal. A rod consistently several percent light is not.
Also check the brand and grade markings rolled into the bar, and ask for the mill test certificate for the heat number on the bundle tag.
How Much Steel Does a House Need?
The quantity comes from the structural drawings and the bar bending schedule. For early budgeting, Indian residential houses use roughly 3.5 to 4.5 kg of steel per sq ft of built-up area, so a 1,500 sq ft house needs roughly 5 to 7 tonnes. The split across sizes is typically weighted towards 8 mm for stirrups and 10 to 12 mm for slabs, with 12 and 16 mm in columns and beams.
The Short Version
Remember D² ÷ 162, keep the 12 mm figure (10.66 kg a rod, 94 a tonne) in your head, and weigh a few rods from every delivery. Converting correctly between rods, kilograms and tonnes is how you check a quote, an invoice and a delivery against each other.
