Rebar Sizes
Structural & HVAC · 9 specs
Direct Answer
Standard reinforcing steel bar (rebar) sizes under ASTM A615 are designated by number sizes #3 through #18 representing the nominal diameter in eighths of an inch (e.g. #4 rebar = 4/8" = 1/2" / 12.7 mm diameter, weighing 0.668 lb/ft).
Source: ASTM A615/A615M-20 Standard Specification for Deformed and Plain Carbon-Steel Bars · Last reviewed Aug 28, 2026
Specs
| Governing Standards | ASTM A615 / ASTM A706 (Earthquake grade) / CSA G30.18 |
| US Numbering System | Rebar number = diameter in 1/8ths of an inch (e.g. #5 = 5/8" / 15.875 mm) |
| #3 Rebar (Driveway / Patio Mesh) | Dia: 0.375 in (9.525 mm) | Area: 0.11 sq in | Weight: 0.376 lb/ft (0.560 kg/m) |
| #4 Rebar (Residential Footings / Walls) | Dia: 0.500 in (12.70 mm) | Area: 0.20 sq in | Weight: 0.668 lb/ft (0.994 kg/m) |
| #5 Rebar (Structural Slabs / Foundation) | Dia: 0.625 in (15.88 mm) | Area: 0.31 sq in | Weight: 1.043 lb/ft (1.552 kg/m) |
| #6 Rebar (Retaining Walls / Beams) | Dia: 0.750 in (19.05 mm) | Area: 0.44 sq in | Weight: 1.502 lb/ft (2.235 kg/m) |
| #8 Rebar (Commercial Columns) | Dia: 1.000 in (25.40 mm) | Area: 0.79 sq in | Weight: 2.670 lb/ft (3.973 kg/m) |
| #18 Rebar (High-Rise Core Columns / Dams) | Dia: 2.257 in (57.33 mm) | Area: 4.00 sq in | Weight: 13.60 lb/ft (20.24 kg/m) |
| Standard Steel Grades | Grade 40 (40 ksi / 280 MPa), Grade 60 (60 ksi / 420 MPa), Grade 75 (75 ksi / 520 MPa) |
Complete ASTM Standard Imperial & Metric Rebar Sizing Matrix
| US Rebar Size | Metric Bar Designation (Soft Metric) | Nominal Diameter (Inches) | Nominal Diameter (mm) | Cross-Sectional Area (sq in) | Unit Weight (lb/ft) | Unit Weight (kg/m) |
|---|---|---|---|---|---|---|
| #3 | #10 | 0.375" (3/8") | 9.525 mm | 0.11 sq in | 0.376 lb/ft | 0.560 kg/m |
| #4 | #13 | 0.500" (1/2") | 12.70 mm | 0.20 sq in | 0.668 lb/ft | 0.994 kg/m |
| #5 | #16 | 0.625" (5/8") | 15.88 mm | 0.31 sq in | 1.043 lb/ft | 1.552 kg/m |
| #6 | #19 | 0.750" (3/4") | 19.05 mm | 0.44 sq in | 1.502 lb/ft | 2.235 kg/m |
| #7 | #22 | 0.875" (7/8") | 22.23 mm | 0.60 sq in | 2.044 lb/ft | 3.042 kg/m |
| #8 | #25 | 1.000" (1") | 25.40 mm | 0.79 sq in | 2.670 lb/ft | 3.973 kg/m |
| #9 | #29 | 1.128" (1-1/8") | 28.65 mm | 1.00 sq in | 3.400 lb/ft | 5.060 kg/m |
| #10 | #32 | 1.270" (1-1/4") | 32.26 mm | 1.27 sq in | 4.303 lb/ft | 6.404 kg/m |
| #11 | #36 | 1.410" (1-3/8") | 35.81 mm | 1.56 sq in | 5.313 lb/ft | 7.907 kg/m |
| #14 | #43 | 1.693" (1-3/4") | 43.00 mm | 2.25 sq in | 7.650 lb/ft | 11.38 kg/m |
| #18 | #57 | 2.257" (2-1/4") | 57.33 mm | 4.00 sq in | 13.60 lb/ft | 20.24 kg/m |
Why Rebar Sizes #9, #10, and #11 Have Odd Decimal Diameters
Up to size #8, rebar diameter strictly equals the number of eighth-inches (d = N / 8). However, sizes #9, #10, and #11 were historically engineered to match the cross-sectional area of square bars:
- #9 Rebar Area: Diameter 1.128 inches yields an area of exactly 1.00 sq in (matching a 1 in × 1 in square bar).
- #10 Rebar Area: Diameter 1.270 inches yields an area of exactly 1.27 sq in (matching a 1-1/8 in square bar).
- #11 Rebar Area: Diameter 1.410 inches yields an area of exactly 1.56 sq in (matching a 1-1/4 in square bar).