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.

Rebar Size Chart

US rebar sizes #3 through #18 — nominal diameter, cross-sectional area and weight, per ASTM A615.

Data verified 2026-09-29 · based on ASTM A615/A615M-20

Quick Answer

The bar number is the diameter in eighths of an inch, so a #4 bar is 4/8 = 0.500 in in diameter. The exception is #9 and larger, where the nominal diameter is specified separately. #5 (0.625 in) is the most common size in residential work.

Find a bar size

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) × d²
weight (lb/ft) = area (in²) × 0.2836 × 12
weight (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.

Value Sources

Each data column on this page is tied to the source it came from. The numbers in square brackets correspond to the table headers above.

#	Source	Type	Revision / method
[1]	ASTM A615 — Standard Specification for Deformed and Plain Carbon-Steel Bars for Concrete Reinforcement	standard	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

Cross-checked against:

Nominal diameters and weights spot-verified at build time against ASTM A615 tabulated values for #4, #5 and #8
Areas independently recomputed from the nominal diameter on every build

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.

Accuracy and use. The values on this page are compiled from the published standards and cross-checked sources listed above. Where values are derived, the derivation is stated. No warranty, express or implied, is made as to the accuracy or completeness of this information, and no liability is accepted for any loss or damage arising from its use. Engineering reference data is provided for guidance in preliminary work — before a value is used for design, fabrication or acceptance testing, verify it against the current revision of the governing standard and against your own inspection. The user assumes all risk and responsibility in connection with the use of this information.

Cite This Page

Every value on this page is traceable to the sources listed above. If you use the data in a document, paper or report, cite it as:

Plain text

Engineering Reference. "Rebar Size Chart." https://refmanual.com/charts/rebar-sizes/ (accessed 2026-09-29). Data from ASTM A615/A615M — Deformed and Plain Carbon-Steel Bars for Concrete Reinforcement, ASTM A615/A615M-20.

BibTeX

@misc{rebar-sizes,
  title        = {Rebar Size Chart},
  author       = {{Engineering Reference}},
  howpublished = {\url{https://refmanual.com/charts/rebar-sizes/}},
  note         = {Accessed: 2026-09-29},
  source       = {ASTM A615/A615M — Deformed and Plain Carbon-Steel Bars for Concrete Reinforcement, ASTM A615/A615M-20}
}

RIS (EndNote, Zotero, Mendeley)

TY  - ELEC
TI  - Rebar Size Chart
AU  - Engineering Reference
PB  - Engineering Reference
UR  - https://refmanual.com/charts/rebar-sizes/
PY  - 2026
DA  - 2026-09-29
N1  - Source: ASTM A615/A615M — Deformed and Plain Carbon-Steel Bars for Concrete Reinforcement, ASTM A615/A615M-20
ER  -

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