How to Calculate the Weight of Steel TMT Rods in Bundles

The construction of modern houses in India cannot be thought of without steel TMT bars. They lend structural integrity to buildings and help in preventing them from collapsing in the event of earthquakes. The BIS Standard IS-1786 from Bureau of Indian Standards (BIS) delineates specifications for high strength deformed steel bars and wires for concrete reinforcement. All reputable companies follow this standard for producing high-quality TMT bars.

When you decide to buy TMT bars for the construction of your house, your architect or construction engineer will ask you to buy “bundles” of TMT bars. He or she will also specify the size of the TMT bar. The number of TMT bars in your bundle will depend on the size of the TMT bars you are getting. Generally, the length of a standard TMT bar is 12 metres; it is the diameter that varies. The diameter can be 8 mm, 10 mm, 12 mm, 16 mm, 20 mm, 25 mm or 32 mm.

In each bundle, the weight of the bars has to be consistent and only slight variations are permissible. This variation is called weight tolerance, and it has to adhere to IS:1786-2008 standard law. it is the following for different sizes of bars-

Sl No.	Nominal Size (mm)	Tolerance On	The Nominal	Mass, Percent
		Batch	Individual Sample	Individual Samples for Coils Only
1	Up to and including 10	± 7	-8	± 8
2	Over 10 upto and including 16	± 5	-6	± 6
3	Over 16	± 3	-4	± 4

The following table shows how many bars will be there 1 bundle for each size -

Size	Soot	Pc/Bundle	Apox Weight/Mtr	Apox Per kg/ weight	Length	Approx Weight/Bundle
8mm	2.5	20	0.395	4.74	12 mtr	94.8
10mm	3	13	0.617	7.4	12 mtr	96.2
12mm	4	9	0.888	10.66	12 mtr	95.9
16mm	5	5	1.58
				18.96	40 ft	94.8
					46 ft	110.8
					50 ft	120.4
20mm	6	3	2.47
				29.62	40 ft	88.86
					46 ft	103.9
					50 ft	112.9
25mm	8	1	3.85
				46.29	40 ft	46.29
					46 ft	54
					50 ft	58.7
28mm	9	1	4.83	58.07	12 mtr	58.07
32mm	10	1	6.31	75.85	12 mtr	75.72

To find out the mass of steel per metre square, the formula is D*D/162. D is the diameter of the bar in metres and the mass will be calculated in kilograms.

For example, if the weight of the bar is 8 mm. Then the mass of the bar per square metre will be -

8*8/162 = 0.396 kg

The weight of 1 TMT bar can be calculated using the following formula -

W = D*D*L / 162

Where W is the weight of the bar in kg, D is the diameter of the bar in mm, and L in the length of the bar in metres.

Now, let us calculate the weight of an 8 mm standard bar.

As per the formula,

W = 8 * 8 * 12 / 162

W = 4.74 kgs

This weight can be different by ± 7% when you actually get TMT bars.

Let us calculate the weight of another bar whose diameter is 25 mm and length is 12 metres. The formula for the same will be -

W = 25 * 25 * 12 / 162

Thus, W = 46.29 kgs

This formula can be used for calculating the weight of any TMT bar, provided you know its diameter and length, and it follows the steel used is of the specified standards.