Nominal diameter, weight per foot and weight per bar — imperial and metric
← Back to the calculatorWeights are nominal ASTM A615 values. Metric bars are named by diameter in millimetres instead.
Every bar is named by its nominal diameter. An imperial bar number is that diameter in eighths of an inch — #3 is 3⁄8 in, or 0.375 in, and #18 is 2.257 in — while a metric bar is named straight out as its diameter in millimetres, from 10 mm to 40 mm. The two systems do not convert exactly, so the chart below gives the diameter in both units.
| Bar | Diameter (in) | Diameter (mm) |
|---|---|---|
| Imperial (US) — bar number = eighths of an inch | ||
| #3 | 0.375 | 9.5 |
| #4 | 0.500 | 12.7 |
| #5 | 0.625 | 15.9 |
| #6 | 0.750 | 19.1 |
| #7 | 0.875 | 22.2 |
| #8 | 1.000 | 25.4 |
| #9 | 1.128 | 28.7 |
| #10 | 1.270 | 32.3 |
| #11 | 1.410 | 35.8 |
| #14 | 1.693 | 43.0 |
| #18 | 2.257 | 57.3 |
| Metric — bar named by its diameter in millimetres | ||
| 10 mm | 0.394 | 10.0 |
| 12 mm | 0.472 | 12.0 |
| 16 mm | 0.630 | 16.0 |
| 20 mm | 0.787 | 20.0 |
| 25 mm | 0.984 | 25.0 |
| 28 mm | 1.102 | 28.0 |
| 32 mm | 1.260 | 32.0 |
| 40 mm | 1.575 | 40.0 |
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The bar number is the diameter in eighths of an inch: a #4 bar is 4⁄8 inch, or 1⁄2 inch. Weights below are the standard nominal values for deformed steel bars (ASTM A615 / A706). Where the rule stops being exact — and what to measure when you need to know what a bar really is — is on the rebar measurement page.
| Bar | Nominal dia. (in) | Weight (lb/ft) | 20 ft bar (lb) | 40 ft bar (lb) | Area (in²) | 40 ft bars / ton |
|---|---|---|---|---|---|---|
| #3 | 0.375 | 0.376 | 7.5 | 15.0 | 0.11 | 133 |
| #4 | 0.500 | 0.668 | 13.4 | 26.7 | 0.20 | 74 |
| #5 | 0.625 | 1.043 | 20.9 | 41.7 | 0.31 | 47 |
| #6 | 0.750 | 1.502 | 30.0 | 60.1 | 0.44 | 33 |
| #7 | 0.875 | 2.044 | 40.9 | 81.8 | 0.60 | 24 |
| #8 | 1.000 | 2.670 | 53.4 | 106.8 | 0.79 | 18 |
| #9 | 1.128 | 3.400 | 68.0 | 136.0 | 1.00 | 14 |
| #10 | 1.270 | 4.303 | 86.1 | 172.1 | 1.27 | 11 |
| #11 | 1.410 | 5.313 | 106.3 | 212.5 | 1.56 | 9 |
| #14 | 1.693 | 7.650 | 153.0 | 306.0 | 2.25 | 6 |
| #18 | 2.257 | 13.600 | 272.0 | 544.0 | 4.00 | 3 |
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Metric bar sizes are given directly as the nominal diameter in millimetres. Weights use the standard density of steel, 7,850 kg/m³.
| Size (mm) | Weight (kg/m) | 12 m bar (kg) | Area (mm²) | 12 m bars / tonne |
|---|---|---|---|---|
| 10 | 0.617 | 7.4 | 79 | 135 |
| 12 | 0.888 | 10.7 | 113 | 93 |
| 16 | 1.578 | 18.9 | 201 | 52 |
| 20 | 2.466 | 29.6 | 314 | 33 |
| 25 | 3.853 | 46.2 | 491 | 21 |
| 28 | 4.834 | 58.0 | 616 | 17 |
| 32 | 6.313 | 75.8 | 804 | 13 |
| 40 | 9.865 | 118.4 | 1,257 | 8 |
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Metric and imperial bar sizes do not convert exactly. These are the pairings most often treated as equivalents in practice:
They are close, but not identical — the areas differ by a few percent, which matters if you are substituting one for the other on a designed job. Substitute only with your engineer's approval.
Three exact factors cover nearly every unit switch on a rebar estimate: 1 in = 25.4 mm (exact), 1 lb/ft = 1.488 kg/m, and 1 in² = 645.16 mm². The same rows as the tables above, converted:
| Bar | lb/ft | kg/m | Area (in²) | Area (mm²) |
|---|---|---|---|---|
| #3 | 0.376 | 0.560 | 0.11 | 71 |
| #4 | 0.668 | 0.994 | 0.20 | 129 |
| #5 | 1.043 | 1.552 | 0.31 | 200 |
| #6 | 1.502 | 2.235 | 0.44 | 284 |
| #7 | 2.044 | 3.042 | 0.60 | 387 |
| #8 | 2.670 | 3.973 | 0.79 | 510 |
| #9 | 3.400 | 5.060 | 1.00 | 645 |
| #10 | 4.303 | 6.404 | 1.27 | 819 |
| #11 | 5.313 | 7.907 | 1.56 | 1,006 |
| #14 | 7.650 | 11.384 | 2.25 | 1,452 |
| #18 | 13.600 | 20.239 | 4.00 | 2,581 |
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Going the other way — a metric supplier quoting kg/m, priced per tonne:
| Metric size | kg/m | lb/ft |
|---|---|---|
| 10 mm | 0.617 | 0.415 |
| 12 mm | 0.888 | 0.597 |
| 16 mm | 1.578 | 1.060 |
| 20 mm | 2.466 | 1.657 |
| 25 mm | 3.853 | 2.589 |
| 28 mm | 4.834 | 3.248 |
| 32 mm | 6.313 | 4.242 |
| 40 mm | 9.865 | 6.629 |
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Two cross-checks catch a fat-fingered conversion. The metric shortcut kg/m ≈ d²/162 (d in mm) gives 0.617 kg/m for 10 mm and 9.877 for 40 mm — both within a rounding of the table. And the diameter check: every US size must land on its own number in eighths, #5 at 5/8 in = 0.625 in = 15.9 mm. If a converted diameter does not match its fraction, the factor was not 25.4.
The tables above are the same for every deformed bar. What changes between the two common ASTM specifications is the steel — above all whether it is built to be welded:
| ASTM A615 | ASTM A706 | |
|---|---|---|
| Built for | General reinforced concrete | Welded and seismic-resisting reinforced concrete |
| Weldable by design | No — chemistry not controlled for welding | Yes — chemistry capped so it welds per AWS D1.4 |
| Grades (min yield, ksi) | 40, 60, 75, 80 in the 2012 edition; 40, 60, 80, 100 in the 2020 edition | 60, 80 only |
| Grade 60 min tensile | 90 ksi (2012 ed.) / 80 ksi (2020 ed.) | 80 ksi |
| Max yield / tensile ratio | Not controlled | 78 ksi max yield, tensile ≥ 1.25 × yield |
| Min elongation, Grade 60 | 9% | 14% |
| Seismic moment frames / walls | Not permitted in special seismic systems | Required by ACI 318 Ch. 18 for special seismic systems |
| Mark | Grade number (e.g. 60) plus mill mark | Grade number plus “W” for weldable steel |
| Sizes, weights, areas | Identical — same #3–#18 nominal tables as on this page | |
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Why it matters on an estimate: the spec does not change the bar count, the weight or the area — a #5 is a #5 either way. It changes what you can do with the bar. Bars that will be welded on site, or are specified in a seismic detail sheet, are called out A706 (usually Grade 60); plain structural slabs, walls and footings are usually A615. The drawing set and the bar mark on the delivered steel are the source of truth; check the mill certificate when the two disagree.
The grade column above is the short version. The full requirement — yield and tensile side by side for Grade 40 to 100, the elongation floor by bar size, and the sizes Grade 40 is actually made in — is in the A615 grade table.
Pick the bar size and spacing, enter your slab or wall dimensions, and the rebar calculator returns the bar count, total length, lap allowance, total weight and a cost estimate. The weight figures it uses are derived the same way as the tables above — from the nominal bar diameter and the density of steel — so they agree to within a fraction of a percent.
If you already know your total length and just want a weight, take the weight per foot from the table above and multiply.