Rebar Size Chart — US #3–#18 & Metric Diameters, Areas, Weights
ASTM A615 rebar sizes #3–#18 with nominal diameter, area, and weight in imperial and metric, plus 6–40 mm metric bars computed from π/4·d²·7850 kg/m³.
Updated August 16, 2026
US reinforcing bars are numbered in eighths of an inch of nominal diameter: a #4 bar is 4/8 = 0.500 in, a #8 bar is 1.000 in. Above #8 the relationship loosens — #9, #10, and #11 diameters are set so the bar area steps evenly, and #14 and #18 are heavy column bars. ASTM A615 also assigns each bar a "soft metric" designation (No. 10 through No. 57) that labels the same physical bar by its approximate diameter in millimetres; nothing about the bar changes, only the name.
The nominal area, not the diameter, is what design calculations use: rebar is deformed, so the nominal dimensions describe a plain round bar of equal weight. Metric bars used with Eurocode and BS practice come in round diameters (8, 10, 12, 16, 20, 25, 32, 40 mm), and their unit mass follows directly from steel density: kg/m = π/4 × d² × 7850 kg/m³ ≈ 0.006165·d² with d in millimetres. The metric table below is computed from that exact formula — the same one the rebar weight calculator uses — not transcribed.
US Bar Sizes #3–#18 (ASTM A615)
| Bar size | Soft metric | Ø (in) | Ø (mm) | Area (in²) | Area (mm²) | Weight (lb/ft) | Mass (kg/m) |
|---|---|---|---|---|---|---|---|
| #3 | No. 10 | 0.375 | 9.5 | 0.11 | 71 | 0.376 | 0.560 |
| #4 | No. 13 | 0.500 | 12.7 | 0.20 | 129 | 0.668 | 0.994 |
| #5 | No. 16 | 0.625 | 15.9 | 0.31 | 200 | 1.043 | 1.552 |
| #6 | No. 19 | 0.750 | 19.1 | 0.44 | 284 | 1.502 | 2.235 |
| #7 | No. 22 | 0.875 | 22.2 | 0.60 | 387 | 2.044 | 3.042 |
| #8 | No. 25 | 1.000 | 25.4 | 0.79 | 510 | 2.670 | 3.973 |
| #9 | No. 29 | 1.128 | 28.7 | 1.00 | 645 | 3.400 | 5.060 |
| #10 | No. 32 | 1.270 | 32.3 | 1.27 | 819 | 4.303 | 6.404 |
| #11 | No. 36 | 1.410 | 35.8 | 1.56 | 1006 | 5.313 | 7.907 |
| #14 | No. 43 | 1.693 | 43.0 | 2.25 | 1452 | 7.650 | 11.384 |
| #18 | No. 57 | 2.257 | 57.3 | 4.00 | 2581 | 13.600 | 20.239 |
Nominal dimensions per ASTM A615/A615M Table 1. #2 (plain) bars are omitted — they are not produced as deformed A615 bars. The soft metric name labels the identical bar.
Metric Bars 6–40 mm (computed)
| Diameter | Area (mm²) | Unit mass (kg/m) |
|---|---|---|
| 6 mm | 28.3 | 0.222 |
| 8 mm | 50.3 | 0.395 |
| 10 mm | 78.5 | 0.617 |
| 12 mm | 113.1 | 0.888 |
| 16 mm | 201.1 | 1.578 |
| 20 mm | 314.2 | 2.466 |
| 25 mm | 490.9 | 3.853 |
| 32 mm | 804.2 | 6.313 |
| 40 mm | 1256.6 | 9.865 |
Computed cells: area = π/4·d², unit mass = π/4·d² × 7850 kg/m³ (≈ 0.006165·d²). Matches published European bar schedules to the displayed precision.
Sources & Further Reading
- ASTM A615/A615M — Standard Specification for Deformed and Plain Carbon-Steel Bars for Concrete Reinforcement, Table 1 (nominal dimensions)
- CRSI Manual of Standard Practice — US bar size, area, and weight tables (cross-check)
- Steel density 7850 kg/m³ per EN 1991-1-1 / common practice — basis of the computed metric unit masses
Frequently Asked Questions
What does the rebar number mean?
For #3 through #8, the number is the nominal diameter in eighths of an inch: #5 = 5/8 in. From #9 up the diameters are chosen so areas step conveniently (a #9 has exactly 1.00 in²), and #14 and #18 are large-format column bars. Metric "soft" names like No. 16 are the same bars relabeled by approximate millimetre diameter.
Why is the nominal diameter of a deformed bar not its measured diameter?
The ribs make the outside of a deformed bar bigger than its nominal size. ASTM A615 defines nominal dimensions as those of a plain round bar with the same weight per foot, which is what matters for area-based design and weight take-offs. Expect the actual outside-of-rib diameter to run roughly 4–7% larger.
How do I convert a metric bar diameter to weight per metre?
Multiply the diameter squared (in mm) by 0.006165: a 16 mm bar is 16² × 0.006165 ≈ 1.578 kg/m. The constant is just π/4 × 7850 kg/m³ expressed per millimetre of diameter, so the same formula works for any round steel bar.
Is a #4 bar the same as a 12 mm bar?
Close but not identical. A #4 bar is 12.7 mm in diameter with 129 mm² of area; a metric 12 mm bar has 113 mm². Substituting one for the other changes the provided steel area by about 12%, so a substitution must be checked against the required area, spacing, and development length, not swapped by feel.
Try the Calculators
Rebar Size Chart — US #3–#18 & Metric Diameters, Areas, Weights — reuven.tools/reference/rebar-sizes — verified against: ASTM A615/A615M — Standard Specification for Deformed and Plain Carbon-Steel Bars for Concrete Reinforcement, Table 1 (nominal dimensions); CRSI Manual of Standard Practice — US bar size, area, and weight tables (cross-check); Steel density 7850 kg/m³ per EN 1991-1-1 / common practice — basis of the computed metric unit masses