Kumar IronCheck 1: the rolled marking
A genuine bar has the brand name, grade (for example 500D) and often the size rolled into the surface. It repeats every metre or so along the length. Painted or stamped marks that rub off, or bars with no marking at all, are a warning sign. Also look for the BIS ISI mark and licence number on the bundle tag.
Check 2: weigh it
Steel is sold by weight, so the weight per metre of a bar tells you whether you are getting the full cross section. The standard formula for weight in kg per metre is d²/162, where d is the diameter in mm. Steel density is 7850 kg/m³, and that gives this formula.
| Diameter | kg per metre | kg per 12 m bar |
|---|---|---|
| 8 mm | 0.395 | 4.74 |
| 10 mm | 0.617 | 7.40 |
| 12 mm | 0.889 | 10.67 |
| 16 mm | 1.580 | 18.96 |
| 20 mm | 2.469 | 29.63 |
| 25 mm | 3.858 | 46.30 |
IS 1786 allows a small tolerance on mass: about plus or minus 7% for bars up to 10 mm, 5% for 12 to 16 mm, and 3% for bars above 16 mm. A bar well below that range is underweight. Weigh a few bars from the bundle, not just one. Our weight chart lists every size.
Check 3: look at the surface
- Ribs should be even, sharp and regular. Worn, uneven or missing ribs reduce the grip between steel and concrete.
- Surface rust that is a thin brown film is normal and rubs off. Deep pitting or flaking scale means the bar has been stored badly.
- Look for cracks, laps, folds or kinks along the length. Straight bars should be reasonably straight.
- Cut a short piece and look at the end: TMT bars show a hard outer ring and a softer core when etched, but you cannot judge this by eye. Do not trust shop-floor acid tricks.
Check 4: the bend and rebend test
IS 1786 requires bars to be bent around a mandrel without cracking on the outside of the bend. On site, ask the contractor to cold bend a spare piece into a hook or U shape. A good bar bends smoothly with no cracks on the outer face. A bar that snaps or shows cracks is brittle and should be rejected. Do not re-bend a bar that has already been bent on the same spot.
Check 5: papers
- Mill test certificate (MTC) with heat number matching the bundle tag. It lists yield strength, tensile strength, elongation and chemistry.
- Tax invoice from an authorised dealer with the brand and grade stated.
- For large orders, send a few samples from the delivered lot to an NABL accredited lab to confirm yield, UTS and elongation against IS 1786.
Common tricks to watch for
- Bars sold as 12 mm that measure closer to 11.5 mm. Check with a vernier caliper across the rib roots.
- Re-rolled or scrap based bars without a proper brand, sold at a lower rate.
- Mixed grades in one bundle, such as Fe415 labelled as Fe500D.
- Wet bundles weighed at the shop: water and mud add a little weight, so weigh dry bars.
Frequently asked questions
- How do I check the weight of a TMT bar?
- Use d²/162 for kg per metre. A 12 mm bar is 0.889 kg per metre, so a 12 m bar is about 10.67 kg. Allow the IS 1786 tolerance for the size.
- Can I test TMT bars at home?
- You can check markings, weight, diameter and do a cold bend test. Yield strength and elongation need a lab test with a universal testing machine.
- Is rust on TMT bars a problem?
- A thin brown film of surface rust is normal and does not hurt bond. Flaking, pitted rust means weakened bars. Scrub off loose rust before casting.
- Which grade should I ask for?
- Fe500D for most houses in west UP, which is seismic zone IV. See our grade comparison guide for the reasoning.