Ribbed Rebar Diameters and Weights per Metre
Weight table from Ø8 to Ø32, the logic behind the 0.006165 × d² formula, 12 m bar weights and a practical way to verify tonnage on site.
Reinforcement tonnage is one of the most critical items in site planning. Underestimate it and work stops; overestimate it and capital sits in the yard. Fortunately the weight of ribbed reinforcing bar can be calculated reliably with a single formula and a small table.
How is weight per metre calculated?
The weight per metre of ribbed rebar is proportional to the square of the diameter. Combining the circular cross-section (π × d² / 4) with the 7850 kg/m³ density of steel gives this practical coefficient:
kg/m = 0.006165 × d² (d: nominal diameter, mm)
For Ø16: 0.006165 × 256 = 1.578 kg/m. The formula works on the nominal diameter; the volume of the ribs is not added, because the standard defines mass on the basis of the nominal diameter.
Standard diameter and weight table (TS 708)
| Diameter | kg/m | Weight of a 12 m bar | Bars per tonne |
|---|---|---|---|
| Ø8 | 0.395 | 4.74 kg | 211 |
| Ø10 | 0.617 | 7.40 kg | 135 |
| Ø12 | 0.888 | 10.66 kg | 94 |
| Ø14 | 1.208 | 14.50 kg | 69 |
| Ø16 | 1.578 | 18.94 kg | 53 |
| Ø18 | 1.998 | 23.98 kg | 42 |
| Ø20 | 2.466 | 29.59 kg | 34 |
| Ø22 | 2.984 | 35.81 kg | 28 |
| Ø25 | 3.853 | 46.24 kg | 22 |
| Ø28 | 4.834 | 58.01 kg | 17 |
| Ø32 | 6.313 | 75.76 kg | 13 |
Straight bar or coil?
Diameters between Ø8 and Ø12 are available both as straight bar and as coil. Coil noticeably reduces waste in workshops equipped with straightening and cutting machines, and has become almost standard for stirrup production. Ø14 and above are usually shipped as 12 m standard bars. Project-specific cutting is possible, but waste and cutting cost should be evaluated together.
Practical tonnage check on site
There is a simple way to verify the tonnage of an incoming delivery: count the bars and multiply by the "weight of a 12 m bar" value from the table.
- 200 bars of Ø16 = 200 × 18.94 = 3,788 kg ≈ 3.79 tonnes
- 150 bars of Ø20 = 150 × 29.59 = 4,439 kg ≈ 4.44 tonnes
A difference of about ±2% between the theoretical value and the weighbridge reading is normal and stems from production tolerances. Larger deviations call for a re-check of diameter measurement and bar count.
Three items often missed in take-off
- Lap lengths: splices in reinforcement usually add 5–8% to total quantities.
- Stirrups and cross ties: easily overlooked because small diameters come in high piece counts; hook allowances must also be added.
- Cutting waste: for short pieces cut from standard bars, waste ranges between 2% and 5% depending on the cutting plan.
Pre-order checklist
- Diameter breakdown and the tonnage required for each size
- Grade: B420C or B500C, according to the structural report
- Form: bar or coil; is cut-to-length required?
- Delivery plan: how many batches and in what sequence?
Why theoretical and actual weights differ
The standard defines mass tolerance by diameter range: the permitted deviation is wider for small diameters and tighter for large ones. In production, rib height, roll wear and cooling conditions create that deviation. The direction of the difference matters too; a batch that is consistently under the theoretical value distorts your take-off systematically and leads to a shortfall on site.
For that reason, checking the total weighbridge figure alone is not enough. Weighing a randomly chosen one-metre sample and comparing it with the kg/m value in the table shows the consistency of the batch in a two-minute check. If the difference is significant, verify the certificate against the heat number and re-measure the diameter.
Storage, rust and tag tracking
A thin dusty rust on ribbed bar does not harm bond; a slightly rough surface can even improve interlock with concrete. The real problem is flaking scale rust: that layer leaves a weak interface between concrete and steel and must be removed with a wire brush.
Store bars on timber blocks away from mud, in separate stacks by diameter and grade. Keeping bundle tags from disappearing on site is critical for matching certificates and for traceability in any future inspection.
Bend allowances and hook lengths
One item is frequently missed in take-off: the length correction after bending. When a bar is bent, the true length measured along the neutral axis is shorter than the sum of the outside dimensions. On small diameters the difference is negligible; at Ø20 and above, on members with many bends, it becomes a meaningful saving.
For stirrup hooks the opposite applies: the hook length and minimum mandrel diameter required by the standards add extra length to the theoretical perimeter. Accounting for both effects when preparing the bar bending schedule largely prevents the familiar "short delivery" surprise on site.
Review the dimension tables for our ribbed reinforcing bar and wire rod coil, and work out mixed-diameter tonnage in seconds with our weight calculator.