How to Calculate the TMT Rods Required for a Building

TMT (Thermo-Mechanically Treated) steel bars are the backbone of RCC construction. Calculating the correct quantity helps avoid steel shortages, excess wastage, and cost overruns.

This guide explains simple site-level methods as well as standard thumb rules used by engineers.

Things You’ll Need

• Structural drawings (if available)

• Built-up area (sq ft or sq m)

• Type of structure (residential / commercial)

• Diameter of TMT bars used

• Unit weight chart for steel

Method 1: Thumb Rule Method (Fast Estimation)

This method is used for initial budgeting before detailed drawings.

Steel Requirement per Square Foot

Type of Building	Steel Quantity
Single-storey house	3.0 – 3.5 kg/sq ft
G+1 Residential	3.5 – 4.0 kg/sq ft
G+2 to G+4 Residential	4.0 – 4.5 kg/sq ft
Commercial building	4.5 – 6.0 kg/sq ft

Example

• Built-up area: 2,000 sq ft

• Steel factor: 4 kg/sq ft

Total steel required = 2,000 × 4 = 8,000 kg (8 tons)

Method 2: Detailed Calculation Using Structural Drawings (Accurate Method)

This is the recommended method for execution.

Step 1: Identify RCC Components

Steel is used in:

• Footings

• Columns

• Beams

• Slabs

• Staircase

Each element has specified bar diameters and spacing.

Step 2: Calculate Steel for Each Component

Formula for Steel Weight

Weight (kg)=

D^2 / 162 X Length ( m )

Where:

• D = Diameter of bar in mm

• 162 = Constant for steel density

  
  

Step 3: Unit Weight of Common TMT Bars

Bar Diameter	Weight (kg/m)
8 mm	0.395
10 mm	0.617
12 mm	0.888
16 mm	1.58
20 mm	2.47
25 mm	3.86

Step 4: Example – Slab Steel Calculation

• Slab size: 5 m × 4 m

• Main bars: 12 mm @ 150 mm spacing

• Distribution bars: 10 mm @ 200 mm spacing

Main bars

• No. of bars = 4 ÷ 0.15 = 27 bars

• Length per bar = 5 m

• Weight = 27 × 5 × 0.888 = 119.88 kg

Distribution bars

• No. of bars = 5 ÷ 0.20 = 25 bars

• Length per bar = 4 m

• Weight = 25 × 4 × 0.617 = 61.7 kg

Total slab steel = 181.58 kg

Method 3: Percentage Method (Quick Site Check)

Steel percentage in RCC:

• Residential buildings: 1% – 1.5% of concrete volume

• Commercial buildings: 1.5% – 2.5%

Example

• Concrete volume: 100 m³

• Steel %: 1.5%

Steel = 100 × 0.015 × 7850 = 11,775 kg

(7850 kg/m³ is steel density)

How Many TMT Rods to Order?

Standard Rod Length

• 1 rod = 12 meters

Example

• Total steel: 8,000 kg

• Using 12 mm bars (0.888 kg/m)

Total length = 8,000 ÷ 0.888 = 9,009 mNumber of rods = 9,009 ÷ 12 ≈ 751 rods

Tips to Reduce Steel Wastage

• Order diameter-wise quantities

• Avoid random cutting on site

• Reuse cut pieces for stirrups

• Maintain bar bending schedules (BBS)

Common Mistakes to Avoid

• Using thumb rules for final execution

• Ignoring lap length and wastage (add 3–5%)

• Mixing different bar grades randomly

• Not matching steel grade with structural design

Final Advice

• Use thumb rules only for cost estimation

• Always rely on structural drawings and BBS for actual procurement

• Consult a structural engineer for multi-storey buildings