Kumar IronUpdated
In this guide
Why weight is the first check
A bar that is thinner than its label has less steel area, so it carries less load than the engineer designed for. It also means you are paying for a 12 mm bar and getting something closer to 11.5 mm. Weight per metre is the quickest way to catch this, because you cannot judge it by eye.
The same steel density applies to every bar, so the nominal weight per metre depends only on the diameter. That is what makes a site check possible.
The formula: d squared divided by 162
Weight in kg per metre is d² divided by 162, where d is the nominal diameter in mm. For 12 mm: 12 x 12 = 144, and 144 / 162 = 0.889 kg per metre. A standard 12 m bar then weighs about 10.67 kg.
The full list is in our TMT bar weight chart. A few common sizes are below.
| Diameter | Kg per metre | Kg per 12 m bar | Bars per tonne (approx.) |
|---|---|---|---|
| 8 mm | 0.395 | 4.74 | 211 |
| 10 mm | 0.617 | 7.40 | 135 |
| 12 mm | 0.889 | 10.67 | 94 |
| 16 mm | 1.580 | 18.96 | 53 |
| 20 mm | 2.469 | 29.63 | 34 |
| 25 mm | 3.858 | 46.30 | 22 |
The 1 metre sample method
- Pick 3 to 5 bars from different places in the bundle, not just the top layer.
- Cut exactly 1 metre from each bar with a hacksaw. Measure with a steel tape, and keep the cut square.
- Weigh each piece on an accurate scale. A kitchen scale is too coarse for small bars. Ask the shop or a nearby kanta for a digital scale that reads to 1 gram or better.
- Average the readings and compare with the table. For 12 mm, the nominal is 0.889 kg, so a 1 m piece around 0.89 kg is right.
If you cannot cut the bars, weigh a full 12 m bar and divide. It is less precise because bars are not always exactly 12 m, so measure the length too.
What tolerance is allowed
IS 1786 allows a small tolerance on the nominal mass. The commonly quoted figures are about plus or minus 7 percent for bars up to 10 mm, 5 percent for 12 to 16 mm, and 3 percent for bars above 16 mm. Those are limits on the average of a lot. The standard separately allows individual bars slightly more.
Online sources do not agree on these bands, so treat them as a working guide, and ask the maker for the clause if there is a dispute. For a 12 mm bar, 5 percent means a 1 m piece should fall between about 0.845 and 0.933 kg.
One bar slightly under is not proof of anything. If the average of your samples sits at or below the lower limit, the bar is underweight.
Weighing a whole bundle
Count the bars in the bundle, multiply by the nominal weight of one bar, and compare with the weighbridge. For example, 94 bars of 12 mm at 10.67 kg each is about 1003 kg. Weigh the truck loaded and empty at a weighbridge near you and note both slips.
Bundles also carry tie wire and sometimes mud or water, so allow a little. A bundle that is a few percent light on the weighbridge, with the tolerance above in mind, is a signal to do the 1 m check as well. Our bundle weight guide explains typical counts.
If the bars are short
- Do not unload until you have taken the samples. Once the steel is in your yard it is harder to return.
- Photograph the bars showing the rolled marks, the cut pieces on the scale and the reading.
- Write the weights on the delivery challan and ask the driver or supervisor to sign it.
- Call the dealer the same day with the numbers. A reputable dealer will check against the maker's mill test certificate and replace or adjust billing.
Frequently asked questions
- Is 12 mm TMT 0.889 kg per metre?
- Yes. 12 squared is 144, divided by 162 gives 0.889 kg per metre, about 10.67 kg for a 12 m bar.
- Can I check weight without cutting the bar?
- Yes, weigh a full bar and measure its length, then divide. It is less accurate than a 1 m cut piece, but it works as a first check.
- Do ribs and rust change the weight?
- Slightly. Heavy rust scale lowers weight once removed. The nominal weight already allows for ribs.
- How many bars should I sample?
- Three to five bars from different parts of the bundle, and from each size if you ordered several.