TMT Bar Weight — kg per metre, per piece, per tonne
Mass per metre for 6 to 32 mm TMT bars, then pieces, bundles and tonnes. Where d²/162 comes from, and the 0.121% it runs heavy by.
Mass per metre for 6 to 32 mm bars, and what that makes of a cutting list: a piece, a bundle, a tonne. The trade divides by 162. The standard the bars are made to divides by 162.196, and this page prints both against the same order.
Every takeoff on an Indian site runs on one number: d²/162 kilograms per metre, for d in millimetres. It is close enough that nobody checks it, and it is not exact. This page shows what it was rounded from, and what the difference is worth on the quantity you are actually ordering.
The mass of a bar is set by its nominal diameter alone. Not by its grade, not by whether it was thermomechanically treated, and not by what a vernier reads across the ribs. Three figures for the same diameter are printed side by side below, because a bill argued over the third decimal is usually an argument about which of the three the two sides used.
| Mass per metre | — |
|---|---|
| All three figures, this diameter | — |
| One piece | — |
| Total length | — |
| Total mass | — |
| Per tonne | — |
| Bundles | — |
| Tolerance IS 1786 allows | — |
| Nominal section | — |
162 is a rounded number, and you can watch it being rounded. IS 1786:2008 clause 3.6 defines nominal mass as the mass of a plain round bar of the nominal diameter at a density of 0.00785 kg per mm² of section per metre, and clause 7.2.1 repeats that figure for checking. That density is 7850 kg/m³. So the mass per metre is 7850 × πd²/4 × 10−6, which rearranges to d² divided by a single constant, 4 ÷ (π × 0.00785), and that constant is 162.1961. Rounding it to 162 makes every trade figure heavy by the same 0.121%, at every diameter, because the error sits in a constant and not in the geometry. On 720 m of 12 mm the trade rule gives 640.00 kg, the unrounded definition 639.23, and Table 1 of the standard 639.36. The table is a third number worth keeping separate: its masses are printed to three significant figures, so the trade rule sits above it at every stocked size except 20 mm, where the rounding went the other way and the rule comes out lighter. Anyone reconciling a bill to the last kilogram should agree which of the three the quantity was taken on before arguing about the steel.
The tolerance the standard allows is fifty times the argument between the two formulas. Table 2 of IS 1786:2008, under clauses 6.2 and 7.2.2, permits a batch to be ±7% off nominal mass up to and including 10 mm, ±5% over 10 up to and including 16 mm, and ±3% over 16 mm. For an individual sample the limits are −8%, −6% and −4%, and a footnote states that for an individual sample the plus tolerance is not specified. Clause 3.1 defines a batch as bars of one size and grade presented for examination and test at one time, which is a testing unit and not your delivery challan. So the 639.36 kg above may lawfully weigh anywhere from 607 to 671 kg. The two formulas argue over 0.64 kg of that. If a load is short, the number that settles it is the weighbridge ticket and the test certificate, not a page like this one.
A bundle is not a unit of anything. IS 1786 clause 3.2 defines a bundle as “two or more coils or a number of lengths properly bound together” and stops there: no piece count, no mass, no table. Clause 13.2 asks only that each bundle or coil carry a tag showing cast or lot number, grade and size. Pieces per bundle is set by the mill, varies with diameter, and changes between plants of the same brand, which is why it is an input here and not a constant. The stock length is in the same position. Clause 7.1 says that where bars are specified cut to a length the deviation shall be within +75/−25 mm, and clause 6.1 lists sizes from 4 to 40 mm with a note that other sizes may be supplied by mutual agreement. Neither clause fixes a length to supply. Twelve metres is the ordinary straight length in the Indian market and 6 and 9 m are traded, with the small diameters often coming in coil, but that is commerce rather than specification, so the default here carries no authority beyond being the common case.
TMT is a process, and it has nothing to do with what the bar weighs. The letters appear in IS 1786:2008 only in Annex A, the informative note on controlled cooling, which describes quenching the bar as it leaves the last rolling stand so that a tempered martensite case forms over a ferrite and pearlite core. The standard's title and its tables are about high strength deformed bars and wires generally. Grade (Fe 415, Fe 500, Fe 550, Fe 600 and the D and S variants) fixes strength and chemistry, not mass: a Fe 550 bar and a Fe 415 bar of the same nominal diameter have the same kilograms per metre, and any quoted “Fe 500 weight chart” that differs from an Fe 415 one at the same size is describing the seller, not the steel. Clause 3.5 is worth reading alongside it: nominal diameter is defined as the diameter of a plain round bar having the same mass per metre as the deformed bar. It is a mass expressed as a length. Calipers laid across the ribs will read over it and calipers laid in the valleys will read under it, and neither reading is the size on the tag.
What this page does not do. It gives no spacing, no lap length, no development length and no bar schedule. Nothing here decides how much steel a member needs or how it is arranged, and quantities computed from a bar bending schedule are only as good as the schedule. The rebar calculator on this site counts bars in a slab and tests a spacing against the ACI 318 ceiling, which is a United States code and carries no weight on an Indian job, where the design documents and the relevant Indian Standards govern. That page is a layout check in imperial sizes and this one is a metric material takeoff. They answer different questions and they should not be substituted for each other.
The standard. IS 1786:2008, High strength deformed steel bars and wires
for concrete reinforcement, Bureau of Indian Standards, read from the Public.Resource.Org mirror
of the BIS text at law.resource.org. Clauses used, all read directly: 3.1 batch, 3.2 bundle, 3.5
nominal diameter, 3.6 nominal mass and the 0.00785 kg/mm² per metre density, 6.1 nominal sizes,
6.2 and Table 1 for nominal mass, 7.1 cutting deviation on a specified length, 7.2.1 the same density
for checking, Table 2 with clauses 6.2 and 7.2.2 for the mass tolerances, 13.2 tagging, and Annex A
for the controlled cooling process. The edition read is 2008; amendments to it exist and were not
read, so whether any amendment alters Table 1 or Table 2 is not something this page can tell you.
What is exact and what is transcribed. The density 0.00785 kg/mm² per metre is the
standard's figure, quoted twice in it. The divisor 162.1961 is arithmetic on that figure and is
exact given it: 4 ÷ (π × 0.00785). The divisor 162 is trade shorthand for the same
thing and appears in no standard. The mass column of Table 1 is transcribed: 0.099, 0.154, 0.222,
0.395, 0.617, 0.888, 1.58, 2.47, 3.85, 4.83, 6.31, 7.99 and 9.86 kg/m for 4, 5, 6, 8, 10, 12, 16, 20,
25, 28, 32, 36 and 40 mm. All thirteen reproduce 0.00785 × πd²/4 to three significant
figures, which is a check the table passes on its own terms.
One column deliberately not transcribed. The cross-sectional area column of Table 1 in the
scan read here does not reproduce πd²/4 at seven of its thirteen sizes: 78.6 against
78.54 mm² at 10 mm, 201.2 against 201.06 at 16 mm, 314.3 against 314.16 at 20 mm, 491.1 against
490.87 at 25 mm, and the same pattern again at 32, 36 and 40 mm. The other six, 4, 5, 6, 8, 12 and
28 mm, agree. The copy is a scan of a printed document and the likeliest
explanation is character recognition rather than the standard, but it cannot be settled from that
copy, so the area printed above is computed as πd²/4 and labelled as computed. Nothing on
this page is derived from that column.
Market convention, sourced to nothing. The 12 m default piece length, the presence of 6 and 9 m
lengths, coiled supply at the small diameters, and every pieces-per-bundle figure. These are what the
Indian market does, they vary by mill, and no standard consulted here fixes any of them. They are
inputs on this page for that reason. If a site publishes a bundle table headed as a specification, ask
which mill it came from.
Worked example
A cutting list line reads 60 pieces of 12 m in 12 mm TMT. What does it weigh, and how many pieces make a tonne?
- IS 1786:2008 Table 1 gives the nominal mass of a 12 mm bar as 0.888 kg/m. That is the standard's own definition worked through: density 0.00785 kg per mm² of section per metre (clause 3.6), which is 7850 kg/m³, times πd²/4 = 113.10 mm², giving 0.887814 kg/m before rounding.
- 60 pieces × 12 m = 720 m. 720 × 0.888 = 639.36 kg, or 0.6394 t. Ten pieces to a bundle makes 6 bundles of 106.56 kg.
- A tonne of 12 mm is 1000 ÷ 0.888 = 1,126.1 m, which is 93.84 pieces of 12 m, so 93 whole pieces and a part.
- The trade rule d²/162 gives 0.888889 kg/m and 640.00 kg for the same 720 m, because 162 is 162.1961 rounded down. That is 0.77 kg over the unrounded definition and 0.64 kg over the 639.36 that Table 1 gives.
639.36 kg on the standard's tabulated nominal mass, 640.00 kg on d²/162, and a tonne holds 93 whole 12 m pieces with 10.1 m of a ninety-fourth left over. The kilogram or so between the formulas is the smallest uncertainty in the line: IS 1786 Table 2 lets a batch of 12 mm run ±5% off nominal mass, so that same order is inside the standard anywhere between 607.39 and 671.33 kg. Pieces per bundle is the mill's convention and not a standard, which is why it is an input.
19 values on this page were driven in a browser and compared with independently derived figures on 2026-09-08 (2035 values across 162 calculators site-wide).
Questions
What is the weight of a 12 mm TMT bar per metre?
0.888 kg per metre, which is the nominal mass IS 1786:2008 tabulates for a 12 mm bar. A 12 m piece is 10.656 kg and a tonne is 1,126 m, or 93 whole pieces of 12 m. The same figure holds for every grade: Fe 415, Fe 500 and Fe 550 of one nominal diameter weigh the same per metre, because grade fixes strength and chemistry rather than section.
Where does the d²/162 formula come from, and is it exact?
It is the standard's own definition with the constant rounded. IS 1786 sets nominal mass from a density of 0.00785 kg per mm² of section per metre, which is 7850 kg/m³, so mass per metre is 7850 × πd²/4 × 10⁻⁶, and that is d² divided by 162.1961. Dividing by 162 instead makes every answer 0.121% heavy against that definition at every diameter: 640.00 kg on 720 m of 12 mm where the unrounded figure is 639.23 kg and the standard's Table 1, printed to three significant figures, gives 639.36 kg.
How many pieces are in a bundle of TMT bar?
There is no standard answer. IS 1786 clause 3.2 defines a bundle as two or more coils or a number of lengths properly bound together, and fixes neither a count nor a mass; clause 13.2 asks only that the bundle carry a tag with the cast or lot number, grade and size. Pieces per bundle is set by the mill and changes with diameter, so this page takes it as an input and multiplies rather than publishing a table.