Reference
Rebar weight chart
Mass per metre, per 12 m bar and per tonne, for every size in the metric range and for ASTM inch-pound bars. The formula is printed above the table, so any row can be checked in about ten seconds.
Written againstIS 1786ASTM A615
Metric bars
The sizes below are the ones rolled to IS 1786 in India and to BS 4449 across the Gulf. Bars are supplied in 12 m lengths in both markets, so that column is usually the one you want when ordering; the per-tonne count is rounded down, because a merchant will not cut you seven-tenths of a bar.
Every figure is nominal. Rolled steel carries a mass tolerance — commonly ±7% on 6 and 8 mm bars, tightening to ±3% at 20 mm and above — so a weighbridge ticket will not match this table exactly, and is not supposed to.
| Barmm | Areamm² | Per metrekg/m | Per 12 m barkg | Bars per tonne12 m |
|---|---|---|---|---|
| 6 | 28 | 0.222 | 2.66 | 375 |
| 8 | 50 | 0.395 | 4.74 | 211 |
| 10 | 79 | 0.617 | 7.40 | 135 |
| 12 | 113 | 0.888 | 10.65 | 93 |
| 16 | 201 | 1.578 | 18.94 | 52 |
| 20 | 314 | 2.466 | 29.59 | 33 |
| 25 | 491 | 3.853 | 46.24 | 21 |
| 28 | 616 | 4.834 | 58.00 | 17 |
| 32 | 804 | 6.313 | 75.76 | 13 |
| 36 | 1018 | 7.990 | 95.88 | 10 |
| 40 | 1257 | 9.865 | 118.38 | 8 |
Where the numbers come from
A reinforcement bar is a steel cylinder. Its mass per metre is its cross-sectional area times its density, and every standard on this page agrees that the density to use is 7850 kg/m³.
That is the whole derivation. Rearranged so the diameter can go in as millimetres, it collapses to a single divisor — and that divisor is where the well-known shortcut comes from.
mass per metre = area × density
= (π/4) · d² · ρ
with d in metres and ρ = 7850 kg/m³
for d in millimetres this rearranges to
kg/m = d² / 162.196… where 162.196… = 4 000 000 / (π × 7850)
20 mm: 400 / 162.196 = 2.466 kg/m
× 12 m = 29.59 kg per bar
1000 / 29.59 = 33 bars per tonneASTM inch-pound bars
American drawings call out bars by number rather than diameter. Up to #8 the number is the diameter in eighths of an inch, so a #4 is a half-inch bar. Above that the pattern breaks: #9, #10, #11, #14 and #18 were sized to give cross-sections of exactly 1, 1¼, 1½, 2¼ and 4 square inches, and their diameters are whatever produced those areas.
That is why this table is quoted rather than computed. ASTM A615 states the nominal mass, and for the large bars recomputing it from the diameter lands up to 0.2% away from the standard's own figure. On a page meant to be copied, the standard wins.
| Bar | Diameterin | Diametermm | Areain² | Per footlb/ft | Per metrekg/m |
|---|---|---|---|---|---|
| #3 | 0.375 | 9.52 | 0.11 | 0.376 | 0.560 |
| #4 | 0.500 | 12.70 | 0.20 | 0.668 | 0.994 |
| #5 | 0.625 | 15.88 | 0.31 | 1.043 | 1.552 |
| #6 | 0.750 | 19.05 | 0.44 | 1.502 | 2.235 |
| #7 | 0.875 | 22.22 | 0.60 | 2.044 | 3.042 |
| #8 | 1.000 | 25.40 | 0.79 | 2.670 | 3.973 |
| #9 | 1.128 | 28.65 | 1.00 | 3.400 | 5.060 |
| #10 | 1.270 | 32.26 | 1.27 | 4.303 | 6.404 |
| #11 | 1.410 | 35.81 | 1.56 | 5.313 | 7.907 |
| #14 | 1.693 | 43.00 | 2.25 | 7.650 | 11.384 |
| #18 | 2.257 | 57.33 | 4.00 | 13.600 | 20.239 |
Using this on an estimate
Take the total cut length of each diameter from the bar bending schedule, multiply by the per-metre figure, and add the sizes together for the tonnage. Laps, hooks and bends belong in the cut length, not in a percentage added afterwards — that is where most disputes over a steel bill start.
What this chart does not include: rolling tolerance, wastage, or the difference between the diameter a bar is sold as and the diameter it measures with the ribs on. None of those is a fixed number, so none of them belongs in a table that gets copied.