Free tool
Steel (TMT) weight calculator
Estimate the weight of TMT steel bars from diameter, length and count. Uses the standard d squared over 162 formula.
How it works
Weight per metre equals the bar diameter in mm squared, divided by 162. Multiply by the total length (length per bar times number of bars) to get the total weight in kilograms.
Typical bar sizes
- 8 to 10 mm for slabs and stirrups
- 12 to 16 mm for beams and columns
- 20 to 25 mm for heavily loaded structural members
Where the d squared over 162 formula comes from
Steel weight per metre is the bar’s cross-sectional area multiplied by the density of steel, about 7,850 kg per cubic metre. Work that through for a round bar and it collapses into one number you can do in your head: diameter squared, divided by 162, gives kilograms per metre. A 12 mm bar is 144 divided by 162, about 0.889 kg per metre. Multiply by total length and you have the weight.
This matters because of a practical mismatch on every site: structural drawings specify steel by length and diameter, while suppliers sell it by weight. This formula is the bridge, and it is the same arithmetic your contractor uses to turn a bar bending schedule into an order.
Weight per metre for common sizes
| Diameter | Per metre | Per 12 m bar | Commonly seen in |
|---|---|---|---|
| 8 mm | 0.395 kg | ~4.7 kg | Stirrups, ties, distribution steel |
| 10 mm | 0.617 kg | ~7.4 kg | Slabs and lighter members |
| 12 mm | 0.889 kg | ~10.7 kg | Slabs and beams, the most ordered size |
| 16 mm | 1.580 kg | ~19.0 kg | Beams and columns |
| 20 mm | 2.469 kg | ~29.6 kg | Columns and heavily loaded beams |
| 25 mm | 3.858 kg | ~46.3 kg | Larger columns and footings |
Those uses are what you commonly see, not a recommendation. Which diameter goes where is decided by your structural engineer from actual loads and spans, and substituting a smaller size to save money is one of the more dangerous economies available on a site.
What this weight excludes
- Lap lengths. Bars are joined by overlapping, and that overlap is real steel your drawing accounts for but a simple length calculation does not
- Cutting waste, since offcuts below usable length are scrap. Allow a few percent when ordering
- Bends, hooks and cranks, which add length to each bar
- Binding wire, cover blocks, chairs and spacers
Frequently asked questions
How much steel does a whole house need?
Very roughly, residential work often lands somewhere around 3 to 4.5 kg per square foot of built-up area, but that band is wide for good reason: spans, floor count, soil conditions and the structural scheme all move it. Use it only as a sanity check on a quotation, never as a design figure. The reliable number is the one in your bar bending schedule.
Is Fe500 heavier than Fe415?
No. The grade describes yield strength, not density, so a 12 mm bar weighs the same in either. A higher grade may allow slightly less steel for the same load, which is a design decision, not a weight one.
Why is my supplier’s weight slightly different?
Rolling tolerances mean actual bar weight varies a little from the theoretical figure, and standards permit a small band either way. Suppliers weigh what they deliver. If the gap exceeds a few percent on a full load, it is worth questioning.