Nominal cross-sectional area and unit mass for reinforcing bar, derived from first principles and cross-checked against ISO 6935-2, BS 4449, IS 1786 and ASTM A615.
Direct answer. Rebar unit mass is not a looked-up constant — it is derived. Multiply the nominal cross-sectional area by the density of steel. A 16 mm bar has an area of 201.1 mm² and a mass of 1.578 kg/m. A US #5 bar has an area of 0.31 in² and a mass of 1.043 lb/ft. Steel density is taken as 7850 kg/m³, equivalently 0.2836 lb/in³.
Total weight for an order or a bar schedule. Runs entirely in your browser.
| Bar | Nominal dia (mm) | Area (mm²) | Mass (kg/m) | Standard (kg/m) | Deviation | Per 12 m bar (kg) |
|---|---|---|---|---|---|---|
| 6 mm | 6 | 28.3 | 0.222 | 0.222 | -0.02% | 2.66 |
| 8 mm | 8 | 50.3 | 0.395 | 0.395 | -0.11% | 4.74 |
| 10 mm | 10 | 78.5 | 0.617 | 0.617 | -0.07% | 7.4 |
| 12 mm | 12 | 113.1 | 0.888 | 0.888 | -0.02% | 10.65 |
| 16 mm | 16 | 201.1 | 1.578 | 1.579 | -0.04% | 18.94 |
| 20 mm | 20 | 314.2 | 2.466 | 2.466 | +0.01% | 29.59 |
| 25 mm | 25 | 490.9 | 3.853 | 3.854 | -0.02% | 46.24 |
| 32 mm | 32 | 804.2 | 6.313 | 6.313 | +0.01% | 75.76 |
| 40 mm | 40 | 1256.6 | 9.865 | 9.864 | +0.01% | 118.38 |
| 50 mm | 50 | 1963.5 | 15.413 | 15.413 | +0.00% | 184.96 |
| Bar | Nominal dia (in) | Area (in²) | Mass (lb/ft) | Standard (lb/ft) | Deviation | Per 20 ft bar (lb) |
|---|---|---|---|---|---|---|
| #3 | 0.375 | 0.11 | 0.376 | 0.376 | -0.03% | 7.52 |
| #4 | 0.5 | 0.20 | 0.668 | 0.668 | +0.03% | 13.36 |
| #5 | 0.625 | 0.31 | 1.044 | 1.043 | +0.10% | 20.88 |
| #6 | 0.75 | 0.44 | 1.504 | 1.502 | +0.10% | 30.07 |
| #7 | 0.875 | 0.60 | 2.046 | 2.044 | +0.12% | 40.93 |
| #8 | 1.0 | 0.79 | 2.673 | 2.67 | +0.11% | 53.46 |
| #9 | 1.128 | 1.00 | 3.401 | 3.4 | +0.03% | 68.02 |
| #10 | 1.27 | 1.27 | 4.311 | 4.303 | +0.19% | 86.22 |
| #11 | 1.41 | 1.56 | 5.314 | 5.313 | +0.02% | 106.28 |
| #14 | 1.693 | 2.25 | 7.661 | 7.65 | +0.15% | 153.22 |
| #18 | 2.257 | 4.00 | 13.616 | 13.6 | +0.12% | 272.31 |
Bar designations #9 and larger have non-round nominal diameters because they derive from the equivalent area of the older square bars. This is a common source of confusion when converting between systems.
Every value in the tables above is computed, not transcribed. The method:
Each derived figure is then compared against the published nominal value in the governing standard. Any bar deviating by more than 1.0% is flagged rather than published silently.
Verification result: all values agree with the published standards. The largest deviation across all 21 bar sizes is 0.19%, which reflects rounding in the published tables rather than a discrepancy in the underlying geometry.
These are nominal masses derived from nominal geometry. Delivered bar is permitted a mass tolerance, and the permitted figure varies by standard and by diameter — check the governing standard for your project rather than assuming a single number, and check the mill certificate for a specific consignment. Deformations (ribs) are already accounted for in the nominal mass convention, so you should not add for them.
We previously quoted specific tolerance percentages here. They were not derived from a standard we had verified, so they have been removed rather than left in place. Everything else on this page is computed and cross-checked.
7850 kg/m³ is the conventional value used by ISO 6935, BS 4449 and IS 1786. The ASTM convention of 0.2836 lb/in³ equals 490 lb/ft³, about 7849 kg/m³ — the same value in different units. The difference between 7850 and 7860 is roughly 0.13%, far inside normal mass tolerance.
Multiply unit mass by total length for each bar size, sum across sizes, then divide by 1000 for metric tonnes or 2000 for US short tons. The calculator above does this for a single bar size. Add a wastage allowance separately, typically 3–5% for cut-and-bend depending on the detailing and the supplier's stock lengths.
Yes for design purposes. The nominal cross-sectional area of a deformed bar is defined as the area of a plain round bar of the same nominal diameter, so the same formula applies to both.