How to check a TMT steel delivery by weight
Steel is sold by the kilo, so weight is the check that counts. Weigh five bars, divide by their length and compare the result with the IS 1786 tables.
By Bulan Sarkar · Updated
Weigh at least five bars of one size together and divide by their total measured length. Compare that kg per metre with IS 1786 Table 1: 8 mm 0.395, 10 mm 0.617, 12 mm 0.888, 16 mm 1.58, 20 mm 2.47, 25 mm 3.85. The lot passes if it is within ±7% for 8 and 10 mm, ±5% for 12 and 16 mm and ±3% above 16 mm (IS 1786:2008 Table 2).
Source: IS 1786:2008, High Strength Deformed Steel Bars and Wires for Concrete Reinforcement (BIS, public.resource.org copy), checked Oct 2026.
Why you weigh bars instead of measuring them
A TMT bar has ribs, so it has no single diameter to measure. IS 1786 gets around this by defining the nominal size through mass: a 12 mm bar is one that weighs the same per metre as a plain round 12 mm rod of steel (clause 3.5). Put calipers across the ribs and you read too much; put them between the ribs and you read too little. Weight per metre gives you one honest number, and it's the same number the price is based on.
A bar that comes in light has less steel in it than its label claims. If the shortfall is inside the tolerance, it's normal rolling variation. If it isn't, you're paying for a size you didn't get, and the engineer's design assumed steel that isn't in the slab.
Where d² ÷ 162 comes from
IS 1786 clause 7.2.1 takes steel as 0.00785 kg per mm² of cross-section per metre of length. A round bar of diameter d has an area of π × d² ÷ 4, so one metre weighs 0.00785 × π ÷ 4 × d² = d² ÷ 162.2 kg. Site engineers round that to d² ÷ 162. For 12 mm: 144 ÷ 162 = 0.889 kg/m, against 0.888 in the standard's own table.
The table below uses the Table 1 figures and the Table 2 batch tolerance. The last column is the most useful one at site: what a single 12 m length should weigh.
| Size | kg/m (Table 1) | Batch tolerance | Accept, kg/m | One 12 m bar, kg |
|---|---|---|---|---|
| 8 mm | 0.395 | ±7% | 0.367 to 0.423 | 4.74 (4.41 to 5.07) |
| 10 mm | 0.617 | ±7% | 0.574 to 0.660 | 7.40 (6.89 to 7.92) |
| 12 mm | 0.888 | ±5% | 0.844 to 0.932 | 10.66 (10.12 to 11.19) |
| 16 mm | 1.58 | ±5% | 1.501 to 1.659 | 18.96 (18.01 to 19.91) |
| 20 mm | 2.47 | ±3% | 2.396 to 2.544 | 29.64 (28.75 to 30.53) |
| 25 mm | 3.85 | ±3% | 3.735 to 3.966 | 46.20 (44.81 to 47.59) |
| 32 mm | 6.31 | ±3% | 6.121 to 6.499 | 75.72 (73.45 to 77.99) |
The check at site, step by step
- Read the tags before unloading. IS 1786 clause 13.2 asks for a tag on every bundle with the cast or lot number, grade and size. The bars should also carry the maker's rolled-in brand mark (clause 13.3). Note the cast number; it's how you match the bars to the test certificate.
- Ask for the test certificate. Clause 12.4 lists what it should show: place of manufacture, size, grade, the rolled-in marking, the cast number, the test date, the mass of the tested lot and the test results.
- Pick five bars of one size from different bundles, not just the top bar of one bundle. Stay well clear while the bundles are lifted down and opened; banded steel springs.
- Measure each bar with a tape. Most bars are cut to 12 m, but write down what you measure. A bar cut short weighs less for an honest reason.
- Weigh them together on a platform scale you trust. The standard weighs and measures to within 0.5%, so a bathroom scale won't do.
- Divide and compare: total kg ÷ total metres gives kg per metre. Compare it with the table above. Repeat for each size in the delivery.
Actual weight or theoretical weight on the bill
Dealers bill steel in one of two ways. Actual weight is what the weighbridge says: loaded truck minus empty truck. Theoretical weight is the bar count × length × the Table 1 figure. A lot can sit inside the tolerance and still weigh 3 to 4% less than its theoretical figure, and if you're billed on theoretical, you pay for steel that never arrived. Ask which basis the quote uses before you order, and keep the weighbridge slip with the invoice.
Worked examples
1. Five 8 mm bars that pass
- 5 bars measured at 12.00 m each = 60.0 m
- Weighed together: 22.4 kg
- 22.4 ÷ 60.0 = 0.373 kg/m against 0.395 nominal
- Difference: −5.5%. The 8 mm band is ±7%
Result: Inside the band. Accept the 8 mm lot.
2. Five 16 mm bars that fail
- 5 bars measured at 12.00 m each = 60.0 m
- Weighed together: 88.0 kg
- 88.0 ÷ 60.0 = 1.467 kg/m against 1.58 nominal
- Difference: −7.2%. The 16 mm band is ±5% (lowest 1.501 kg/m)
Result: Outside the band. Hold the 16 mm bundles, show the dealer the figures and tell your engineer before any of it is cut.
3. A truck of 12 mm billed on theoretical weight
- Invoice: 94 bars × 12 m = 1,128 m × 0.888 = 1,001.7 kg theoretical
- Weighbridge slip: 962 kg actual
- 962 ÷ 1,001.7 = −4.0%, inside the ±5% band
- Gap: 39.7 kg × ₹55 to 68/kg (TMT band, Jul 2026) = about ₹2,200 to ₹2,700
Result: The steel passes, but a theoretical-weight bill charges for 39.7 kg you didn't receive. Ask for actual-weight billing.
Tips and tricks
- Weigh bars from at least two bundles. One light bundle tells you more than the average of a whole truck.
- Do the check before unloading is finished. A truck that has left can't be weighed empty, and the slip loses its meaning.
- Keep the bundle tags. They carry the cast number, and you'll want it if a question comes up after the slab is cast.
- Write the weights in the site register the same day: size, bars, metres, kg, kg/m and the cast number.
- Cut-to-length or bent bars can't be checked against a 12 m figure. Weigh a straight offcut of known length instead (the standard uses pieces of at least 0.5 m).
What we would do
We'd agree actual-weight billing when ordering, then weigh five bars of every size on the first delivery from a new dealer, with the results in the site register. If a size comes in outside the Table 2 band, keep those bundles apart and uncut until your engineer and the dealer have seen the numbers. Once a dealer has passed two deliveries, checking one size per truck is usually enough.
Frequently asked questions
What is the weight tolerance for TMT bars as per IS 1786?
How much should a 12 m length of 12 mm TMT bar weigh?
Is d²/162 exact?
Can I check the diameter with a vernier caliper instead?
Sources and date checked
- IS 1786:2008, clauses 3.5, 7.2, 12.4, 13 and Tables 1 and 2 (public.resource.org copy). Checked Oct 2026.
- IS 4082:1996, Stacking and Storage of Construction Materials at Site, clause 4.13 (steel). Checked Oct 2026.
This guide checks that the delivery matches the order. Bar sizes, grades and spacing come from your structural engineer's drawing, and only the engineer decides whether steel that fails a check can be used.