Unit Weight of Steel: Formula and TMT Bar Chart
The unit weight of steel is 7,850 kg/m³. For a round bar, weight per metre ≈ D²/162 kg, with D in mm.
IS 1786 lists 8 mm at 0.395 kg/m, 10 mm at 0.617, 12 mm at 0.888 and 16 mm at 1.58 kg/m. A full 12 m length of 12 mm bar weighs 10.656 kg.
For house and RCC quantities, use the steel weight calculator; for cutting lengths, use the BBS calculator. Price the result with steel rates per kg and tonne.
Weight from diameter, length and bar count
Enter one diameter and the actual length of each bar for total kg and tonnes.
106.538 kg · 0.106538 tonnes
0.887814 kg/m using circular area × 7,850 kg/m³.
D²/162 shortcut: 106.667 kg. No laps, hooks or cutting waste added.
TMT bar weight chart: 6 mm to 40 mm
Each row is the IS 1786 nominal mass per metre, multiplied by 12 m for one full bar.
| Diameter (mm) | Nominal kg/m | kg per 12 m bar | 12 m bars per tonne |
|---|---|---|---|
| 6 | 0.222 | 2.664 | 375.38 |
| 8 | 0.395 | 4.740 | 210.97 |
| 10 | 0.617 | 7.404 | 135.06 |
| 12 | 0.888 | 10.656 | 93.84 |
| 16 | 1.58 | 18.960 | 52.74 |
| 20 | 2.47 | 29.640 | 33.74 |
| 25 | 3.85 | 46.200 | 21.65 |
| 28 | 4.83 | 57.960 | 17.25 |
| 32 | 6.31 | 75.720 | 13.21 |
| 36 | 7.99 | 95.880 | 10.43 |
| 40 | 9.86 | 118.320 | 8.45 |
Source: IS 1786:2008, Table 1, printed page 5. Bar counts are fractional equivalents. The chart assumes 12 m bars; use the supplied length for orders.
The calculator uses unrounded circular area, matching our steel calculator. The chart uses the standard's printed masses: for example, 16 mm is 1.58 kg/m here versus about 1.578336 kg/m by circular area.
Deriving D²/162 from 7,850 kg/m³
D²/162 is a bar's cross-section area × 1 m × 7,850 kg/m³, with the true divisor (about 162.196) rounded to 162.
Mass per metre = (π/4) × (D/1,000)² × 1 × 7,850 kg
= (π × 7,850 / 4,000,000) × D² kg/m
≈ 0.006165375583 × D² ≈ D²/162.196 kg/m
Site shortcut: D²/162 kg/m
The rounded divisor gives about 0.121% more than the circular-area figure. IS 1786 clause 7.2.1 gives the density basis as 0.00785 kg per mm² of section per metre, equivalent to 7,850 kg/m³.
Worked example, ten 12 mm bars, each 12 m: (π/4) × 0.012² × 12 × 10 × 7,850 ≈ 106.54 kg (0.1065 tonne). The shortcut gives (12²/162) × 12 × 10 ≈ 106.67 kg. The IS table gives 0.888 × 12 × 10 = 106.56 kg.
IS 1786 mass tolerances by diameter
A batch of bars may weigh up to 7% more or less than nominal for sizes up to 10 mm, 5% for over 10 to 16 mm, and 3% above 16 mm.
| Nominal diameter | Batch | Individual sample (one bar) | Coil sample |
|---|---|---|---|
| Up to and including 10 mm | ±7% | Up to 8% under; no upper limit set | ±8% |
| Over 10, up to and including 16 mm | ±5% | Up to 6% under; no upper limit set | ±6% |
| Over 16 mm | ±3% | Up to 4% under; no upper limit set | ±4% |
The Table 2 footnotes say one sample taken from a batch does not count as an “individual sample”, and coils have no batch tolerance. Under clause 7.2.2 these limits apply unless the manufacturer and purchaser agree otherwise.
Example: a 12 mm batch has nominal mass 0.888 kg/m and ±5% tolerance, giving 0.888 × 0.95 = 0.8436 to 0.888 × 1.05 = 0.9324 kg/m. An individual 12 mm sample must not be lighter than 0.888 × 0.94 = 0.8347 kg/m. Judge a batch by the standard's sampling, not a single rod.
Steel plates and sections
For a steel plate, mass = 7,850 × length × width × thickness, with all dimensions in metres.
A 1 m × 1 m × 10 mm plate is 7,850 × 1 × 1 × 0.010 = 78.5 kg. For rolled or hollow sections, use the manufacturer's verified cross-sectional area or section mass; outer width × depth would wrongly count empty space as steel.
Frequently asked questions
What is the unit weight of steel?
7,850 kg/m³. IS 1786:2008 uses this density to check bar mass. For a round bar of diameter D in mm, weight per metre is about D²/162 kg. A 12 mm bar is 0.888 kg/m in the IS 1786 table.
What are the weights of 8 mm, 10 mm, 12 mm and 16 mm rods per metre?
IS 1786:2008 Table 1 gives 0.395 kg/m for 8 mm, 0.617 kg/m for 10 mm, 0.888 kg/m for 12 mm and 1.58 kg/m for 16 mm. Multiply by the actual length in metres for one rod.
How many 12 mm bars are in one tonne?
About 94. One 12 m bar of 12 mm weighs 0.888 × 12 = 10.656 kg, and 1,000 ÷ 10.656 = 93.84. At nominal mass, 93 bars weigh 991.0 kg and 94 bars weigh 1,001.7 kg. The count you actually get depends on the bars’ weighed mass.
Why do D²/162 and the IS table give slightly different weights?
D²/162 is a rounded shortcut; the circular-area figure is about D²/162.196. IS 1786 prints its own rounded nominal masses. Pick one basis and use it throughout a bill or estimate.
Does Fe 500 weigh more than Fe 550 at the same diameter?
No. Nominal mass depends only on diameter and steel density, so Fe 500 and Fe 550 bars of the same size have the same chart weight. Actual bars can vary within the IS 1786 mass tolerances.
Can I use this chart for billing or checking a delivery?
Yes, if your contract bills on nominal weight. For actual mass, divide the weighed mass by the measured length. One bar cannot prove a batch passes: follow the IS 1786 sampling rules and check the mill test certificate.
Have a measured bar schedule? Use the steel weight calculator to turn the lengths into a project quantity.