Sources and scope for this page: ASTM A615/A615M-20, covering nominal diameters and nominal weights for #3 through #18. No independent source check is recorded for this page: the content rests on the sources listed and on the working shown on the page. Full sources, values and limits on this page.
Page last changed 2026-10-19 · based on ASTM A615/A615M-20
Quick Answer
US Rebar Sizes and Weights (ASTM A615)
| Bar size[1] | Diameter in[1] | Diameter mm[3] | Area in²[2] | Area mm²[2] | Weight lb/ft[1] | Weight kg/m[4] |
|---|---|---|---|---|---|---|
| #3 # | 0.375 | 9.525 | 0.110 | 71 | 0.376 | 0.560 |
| #4 # | 0.500 | 12.700 | 0.196 | 127 | 0.668 | 0.994 |
| #5 # | 0.625 | 15.875 | 0.307 | 198 | 1.043 | 1.552 |
| #6 # | 0.750 | 19.050 | 0.442 | 285 | 1.502 | 2.235 |
| #7 # | 0.875 | 22.225 | 0.601 | 388 | 2.044 | 3.042 |
| #8 # | 1.000 | 25.400 | 0.785 | 507 | 2.670 | 3.973 |
| #9 # | 1.128 | 28.651 | 0.999 | 645 | 3.400 | 5.060 |
| #10 # | 1.270 | 32.258 | 1.267 | 817 | 4.303 | 6.404 |
| #11 # | 1.410 | 35.814 | 1.561 | 1007 | 5.313 | 7.907 |
| #14 # | 1.693 | 43.002 | 2.251 | 1452 | 7.650 | 11.384 |
| #18 # | 2.257 | 57.328 | 4.001 | 2581 | 13.600 | 20.239 |
Bar numbers #3 through #8 are the nominal diameter in eighths of an inch. From #9 upward the nominal diameter is specified separately and no longer falls exactly on an eighth — #9 is 1.128 in rather than 1.125 in. Area is computed from the nominal diameter; weight is computed from the area at 0.2836 lb/in³.
How Bar Numbers Work
For the common sizes the bar number is simply the diameter in eighths of an inch: #3 is 3/8 in, #4 is 4/8 in, #8 is 8/8 in. This breaks down above #8, where the sizes were set separately and the numbers became labels rather than measurements — #9 is 1.128 in, not 1.125 in, and #14 is 1.693 in, well short of 14/8.
Metric practice uses the nominal diameter directly: a #5 bar is designated 16 mm in metric drawings, from its 15.875 mm nominal diameter.
Weight and Area Relationships
Both derived columns come from the nominal diameter, so they are internally consistent with it:
area = (π/4) × d²weight (lb/ft) = area (in²) × 0.2836 × 12weight (kg/m) = weight (lb/ft) × 0.453592 ÷ 0.3048
Weight per unit length is what rebar is actually bought and priced on, so it is the column to use for takeoffs. Because the nominal diameter carries a manufacturing tolerance, actual bar weight can differ slightly from the tabulated figure.
Frequently Asked Questions
- What size is #4 rebar?
- #4 rebar is 0.500 in (12.700 mm) in nominal diameter, with a cross-sectional area of 0.196 in² and a weight of 0.668 lb/ft. The bar number is the diameter in eighths of an inch.
- What size is #5 rebar?
- #5 rebar is 0.625 in (15.875 mm) in diameter, 0.307 in² in area, and weighs 1.043 lb/ft. It is the most common bar size in residential foundations and slabs.
- How much does #4 rebar weigh per foot?
- 0.668 lb/ft, or 0.994 kg/m. Weight per foot is computed from the nominal area at a steel density of 0.2836 lb/in³, so it scales with the square of the diameter.
- What is the largest rebar size?
- ASTM A615 standardises up to #18, at 2.257 in (57.3 mm) nominal diameter and 13.600 lb/ft. Larger sections are normally specified as structural steel rather than rebar.
- Why is #9 rebar 1.128 inches and not 1.125?
- Because above #8 the sizes were set as separate specifications rather than as eighths of an inch. The bar number became a label. #9 through #18 all deviate from n/8 to some degree.
- Does rebar size affect concrete cover requirements?
- Yes — cover requirements are stated as a minimum distance from the concrete surface to the bar, and larger bars have a larger radius, so the same cover leaves the bar centre further in. The governing requirement is in the applicable building code, not in the bar dimension table.
Related
Value Sources
References and calculation methods used for this page are listed below. Numbered markers connect table columns where present. A reference listing does not itself establish that every value has been independently checked.
| # | Source | Type | Revision / method |
|---|---|---|---|
| [1] | ASTM A615 — Standard Specification for Deformed and Plain Carbon-Steel Bars for Concrete Reinforcement | reference | ASTM A615/A615M-20 — source |
| [2] | Cross-sectional area | derived | area = (π/4) × nominal diameter². |
| [3] | Millimetre conversion | derived | Inch value × 25.4. |
| [4] | Weight per unit length | derived | weight (lb/ft) = area (in²) × 0.2836 × 12; kg/m = lb/ft × 0.453592 ÷ 0.3048. |
Data Sources
| Standard | Revision | What it covers on this page |
|---|---|---|
| ASTM A615/A615M — Deformed and Plain Carbon-Steel Bars for Concrete Reinforcement | ASTM A615/A615M-20 | nominal diameters and nominal weights for #3 through #18 |
Verification scope
No page-specific independent source review is recorded here. The listed references and formulas explain the basis of the compilation; automated consistency checks do not verify the original sources or establish product conformity.
Derived values — the following values on this page are calculated, not taken directly from the standard:
| Value | How it is derived |
|---|---|
| Area, millimetre conversions and weight in kg/m | Computed from the nominal diameter and tabulated weight — see the formulas above. |
Nominal values. Actual bar dimensions and weights carry manufacturing tolerances, and deformed bar is specified by nominal area rather than measured diameter for design purposes.
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