Steel Required per sq ft and the TMT Bar Weight Formula (D²/162)
Convert bar diameters to weight in seconds, and estimate how much steel a building needs before the structural drawings are final.
The weight of a steel bar in kg per metre is D²/162, where D is the diameter in mm. So an 8 mm bar weighs about 0.395 kg/m, 10 mm about 0.617 kg/m, 12 mm about 0.889 kg/m and 16 mm about 1.58 kg/m. For budgeting, residential RCC buildings typically use about 3.5–4.5 kg of steel per sq ft of built-up area; exact quantities come from the bar bending schedule.
The D²/162 formula
The density of steel is about 7,850 kg/m³. The weight of a 1 m long round bar of diameter D (mm) is:
Weight (kg/m) = D² ÷ 162
(It comes from π/4 × D² × 7850 ÷ 10⁶ ≈ D²/162.2.)
TMT bar weight chart
| Diameter (mm) | kg per metre | kg per 12 m bar | Bars per tonne (12 m) |
|---|---|---|---|
| 8 | 0.395 | 4.74 | ~211 |
| 10 | 0.617 | 7.40 | ~135 |
| 12 | 0.889 | 10.67 | ~94 |
| 16 | 1.580 | 18.96 | ~53 |
| 20 | 2.469 | 29.63 | ~34 |
| 25 | 3.858 | 46.30 | ~22 |
| 32 | 6.321 | 75.85 | ~13 |
Actual weights vary slightly within the rolling tolerance allowed by IS 1786.
Steel thumb rule per sq ft
For budgeting a typical residential RCC frame:
| Building type | Steel per sq ft of built-up area |
|---|---|
| Individual house, G / G+1 | ~3.5–4.5 kg |
| Low-rise apartments | ~4–5 kg |
| Commercial / high-rise | Higher; design-dependent |
So a 1000 sq ft house usually needs about 3.5 to 4.5 tonnes of steel.
Steel per cubic metre of concrete (by element)
| Element | Typical steel | kg per m³ (approx.) |
|---|---|---|
| Footings | ~0.5–1% | ~40–80 |
| Slabs | ~0.7–1% | ~55–80 |
| Beams | ~1–2% | ~80–160 |
| Columns | ~1–4% | ~80–300 |
These are wide ranges. Always order from the bar bending schedule (BBS) — a thumb rule can easily be 20% off for a particular design.
Worked example
You need 60 bars of 12 mm, each 12 m long:
- Weight = 60 × 12 × 0.889 = 640 kg
Ordering tips
- Order by weight with bar counts per diameter from the BBS.
- Allow 2–3% wastage for cut lengths and laps.
- Check grade (Fe 500, Fe 500D, Fe 550D) matches the drawing. See TMT grades explained.
- Store bars off the ground and covered; see how to check TMT quality.
Browse TMT bars or request a quote with your BBS.
Key takeaways
- Bar weight (kg/m) = D²/162.
- 12 mm = 0.889 kg/m; 16 mm = 1.58 kg/m.
- Budget 3.5–4.5 kg of steel per sq ft for houses.
- Order from the BBS, not thumb rules.
Frequently asked questions
What is the formula for steel bar weight?
Weight in kg per metre equals D²/162, where D is the bar diameter in millimetres.
What is the weight of a 12 mm TMT bar?
About 0.889 kg per metre, or roughly 10.67 kg for a standard 12 m bar.
How much steel is required per sq ft?
Typical residential RCC buildings use about 3.5–4.5 kg per sq ft of built-up area for budgeting purposes.
How many 8 mm bars are in one tonne?
About 211 bars of 12 m length, since each weighs roughly 4.74 kg.
Need materials for this work?
See indicative delivered prices for your pincode, or get an itemised project quotation with freight, unloading and GST shown line by line.
This guide is general information for planning and buying. Quantities, grades and methods for your structure must follow your approved drawings, your engineer’s specification and the applicable Indian Standards.
