US ASTM vs Metric Rebar Size Crosswalk Table
Reinforcing steel standards differ significantly between North American (US ASTM) and international (Metric ISO/BS/SASO) systems. In the United States, rebar is categorized by size numbers (#3 through #18) representing nominal diameters in eighths of an inch. Internationally, rebar is classified directly by its nominal diameter in millimeters. Use this engineering-grade crosswalk to compare dimensions, areas, and weight specifications side-by-side.
Rebar Weight & Dimension Comparison Crosswalk
| US Size | Metric Equivalent | Nominal Diameter (in) | Nominal Diameter (mm) | Area (in²) | Area (mm²) | Unit Weight (lb/ft) | Unit Mass (kg/m) |
|---|---|---|---|---|---|---|---|
| #3 | 10mm | 0.375 in | 9.52 mm | 0.11 in² | 71 mm² | 0.376 lb/ft | 0.395 kg/m (for 8mm: 0.395, 10mm: 0.617) |
| #4 | 12mm | 0.500 in | 12.70 mm | 0.20 in² | 129 mm² | 0.668 lb/ft | 0.888 kg/m |
| #5 | 16mm | 0.625 in | 15.88 mm | 0.31 in² | 200 mm² | 1.043 lb/ft | 1.578 kg/m |
| #6 | 20mm | 0.750 in | 19.05 mm | 0.44 in² | 284 mm² | 1.502 lb/ft | 2.466 kg/m |
| #7 | 22mm | 0.875 in | 22.23 mm | 0.60 in² | 387 mm² | 2.044 lb/ft | 2.984 kg/m |
| #8 | 25mm | 1.000 in | 25.40 mm | 0.79 in² | 509 mm² | 2.670 lb/ft | 3.853 kg/m |
| #9 | 28mm | 1.128 in | 28.65 mm | 1.00 in² | 645 mm² | 3.400 lb/ft | 4.834 kg/m |
| #10 | 32mm | 1.270 in | 32.26 mm | 1.27 in² | 819 mm² | 4.303 lb/ft | 6.313 kg/m |
| #11 | 36mm | 1.410 in | 35.81 mm | 1.56 in² | 1006 mm² | 5.313 lb/ft | 7.990 kg/m |
| #14 | 40mm | 1.693 in | 43.00 mm | 2.25 in² | 1452 mm² | 7.650 lb/ft | 9.865 kg/m |
| #18 | 50mm | 2.257 in | 57.33 mm | 4.00 in² | 2581 mm² | 13.600 lb/ft | 15.413 kg/m |
How Rebar Equivalencies are Computed
US rebar sizes represent the bar's nominal diameter in eighths of an inch. For example, a **#4 bar** has a diameter of 4/8 = 0.500 inches. To convert this nominal diameter to millimeters, multiply by 25.4: 0.500 in × 25.4 = 12.7 mm Under metric standards, the nearest nominal standard diameter is **12mm** (governed by BS 4449 and ISO 6935-2).
Due to minor variations in nominal diameter rounding between standards, the weights do not align perfectly. For example:
• US #4 rebar has a unit weight of **0.668 lb/ft** (which converts to **0.994 kg/m**).
• Metric 12mm rebar has a nominal unit mass of **0.888 kg/m** (using the international standard mass rate).
For heavy structural engineering computations, always calculate using the exact weight table specified by local codes (such as ACI 318 in the US or SASO/GSO in the Gulf region).