TMT Steel Rod Weight Chart & Roof Slab Cost Guide (2026, India & West Bengal)
Building a home is probably the biggest spend of your life, and steel is where a lot of that money quietly goes. Order too little and work stops halfway. Order too much, and you’re left with rusting rods and a lighter wallet.
So how do you work out the exact weight of the TMT bars you need, and what a roof slab will really cost? That’s what this guide covers. Whether you’re building in West Bengal or anywhere else in India, you’ll get the standard weight chart, a simple formula you can use on site, and a practical way to budget for your 2026 slab.
Why Getting Your TMT Steel Estimate Right Matters
TMT (Thermo-Mechanically Treated) bars are the skeleton of every RCC (Reinforced Cement Concrete) structure. They carry the tensile load that concrete can’t, which is what lets a building handle heavy loads, seismic activity, and weather.
Buying steel on a contractor’s rough guess rarely ends well. You either run short mid-construction or pay for surplus you never use. Engineers avoid this by working from standard unit weights, and you can too.
1. TMT Steel Bar Weight Chart (IS 1786 Standard)
Rebar in India follows IS 1786, and a bar’s weight depends directly on its nominal diameter. Here are the figures for the most common sizes:
- 8 mm bar
- Unit weight: 0.395 kg/meter
- Weight per 12 m rod: 4.74 kg
- Typical use: Stirrups, rings, and light distribution steel.
- 10 mm bar
- Unit weight: 0.617 kg/meter
- Weight per 12 m rod: 7.40 kg
- Typical use: Secondary slab reinforcement and lintels.
- 12 mm bar
- Unit weight: 0.888 kg/meter
- Weight per 12 m rod: 10.66 kg
- Typical use: Beams, columns, and main slab reinforcement.
- 16 mm bar
- Unit weight: 1.579 kg/meter
- Weight per 12 m rod: 18.95 kg
- Typical use: Heavy columns, footings, and primary beams.
- 20 mm and above
- Used in commercial buildings, high-load columns, and heavy foundations.
2. The D²/162 Formula: Calculate Any Bar’s Weight in Seconds
You don’t need to memorise the chart. One formula gives you the weight per meter of any steel bar:
Weight (kg/meter) = D² ÷ 162
Here, D is the bar’s nominal diameter in millimeters.
Take a 12 mm bar: (12 × 12) ÷ 162 = 144 ÷ 162 = 0.888 kg/meter. Multiply by the length and you have the total weight.
If you’d rather skip the arithmetic, try our free TMT Steel Rod Weight Calculator. Enter your dimensions, and it does the rest.
3. Roof Slab Cost Estimation (2026, India & West Bengal)
A roof slab isn’t just steel. Your budget has to cover TMT bars, cement, stone chips, sand, shuttering, and labor. As a rough rule of thumb, an RCC building uses about 3.5 to 5 kg of TMT steel per square foot of built-up area, depending on the design loads and your seismic zone. Your structural engineer’s drawings always override this number.
What Goes Into the Cost
- Steel: Usually 30% to 35% of the structural cost, so it’s the line item worth watching most closely.
- Concrete mix (M20/M25): Most residential slabs use M20, typically at a 1:1.5:3 ratio (cement: sand: aggregate). It gives the compressive strength a house needs.
- Shuttering and labor: Rates vary across West Bengal and the rest of India, and they depend largely on whether your contractor uses wooden or steel plate staging. Get at least two quotes.
Frequently Asked Questions (FAQ)
1. How much does a 12-meter TMT rod weigh?
It depends on the diameter. A 12 mm bar weighs 0.888 kg per meter, so a full 12 m rod comes to about 10.66 kg. Use the D²/162 formula above for other sizes.
2. How many 10 mm TMT bars come in a bundle?
It varies a little by manufacturer, but a bundle of 10 mm bars usually holds around 7 pieces. Check with your supplier before you order.
3. How can I calculate steel requirements without making mistakes?
Use the D²/162 formula for single bars, or use the free calculator to work out weights for your whole project at once.