REBAR SIZE CHART: US AND MEXICAN DESIGNATIONS COMPARED
By Virginia Viadas
Rebar is sized by number in both the United States and Mexico, and the numbers look identical — until they aren't. In the Mexican system the designation number equals the nominal diameter in eighths of an inch across the full range. In the US system that holds only through #8. Above that, the numbers follow equivalent square-bar areas instead. Ordering #10 bar in Monterrey and #10 bar in Houston gets you two different products.
US rebar sizes (ASTM A615 / A706)
| Size | Nominal diameter (in) | Nominal diameter (mm) | Area (in²) | Weight (lb/ft) | Soft metric |
|---|---|---|---|---|---|
| #3 | 0.375 | 9.5 | 0.11 | 0.376 | #10 |
| #4 | 0.500 | 12.7 | 0.20 | 0.668 | #13 |
| #5 | 0.625 | 15.9 | 0.31 | 1.043 | #16 |
| #6 | 0.750 | 19.1 | 0.44 | 1.502 | #19 |
| #7 | 0.875 | 22.2 | 0.60 | 2.044 | #22 |
| #8 | 1.000 | 25.4 | 0.79 | 2.670 | #25 |
| #9 | 1.128 | 28.7 | 1.00 | 3.400 | #29 |
| #10 | 1.270 | 32.3 | 1.27 | 4.303 | #32 |
| #11 | 1.410 | 35.8 | 1.56 | 5.313 | #36 |
| #14 | 1.693 | 43.0 | 2.25 | 7.65 | #43 |
| #18 | 2.257 | 57.3 | 4.00 | 13.60 | #57 |
Mexican rebar sizes (varilla corrugada, NMX-C-407-ONNCCE / NMX-B-506-CANACERO)
| Designación | Diámetro nominal | Equivalent |
|---|---|---|
| 2.5 | 6.4 mm | 1/4 in |
| 3 | 9.5 mm | 3/8 in |
| 4 | 12.7 mm | 1/2 in |
| 5 | 15.9 mm | 5/8 in |
| 6 | 19.1 mm | 3/4 in |
| 8 | 25.4 mm | 1 in |
| 10 | 31.8 mm | 1 1/4 in |
| 12 | 38.1 mm | 1 1/2 in |
The Mexican standard's own marking examples confirm the logic: designation 10 corresponds to a 1 1/4-inch nominal diameter, and designation 12 to 1 1/2 inches. That is not true of US #10 or #11.
Where the two systems diverge
- Through #8 they match. A Mexican No. 4 and a US #4 are both nominal 1/2 inch. Substitution across the border is straightforward in this range.
- From #9 up they do not. Confirm nominal diameter, not designation number, on any bar above 1 inch.
- Above No. 12, verify against the mill's ficha técnica. Designations 14, 16 and 18 exist in the Mexican standard but do not map cleanly onto US #14 and #18.
Grades: what "Grade 42" actually means
US grades are stated in ksi: Grade 60 means 60,000 psi minimum yield. Mexican grades are stated in kgf/mm² shorthand: Grade 42 corresponds to roughly 4,200 kg/cm² yield, which is approximately 60,000 psi — so Mexican Grade 42 and US Grade 60 are broadly comparable in yield strength, though not interchangeable without verifying the governing standard.
| Mexican grade | Approx. yield | Availability under the standard |
|---|---|---|
| Grado 30 | ~3,000 kg/cm² | Designations 3 through 6 only |
| Grado 42 | ~4,200 kg/cm² | Full commercial range; the market default |
| Grado 52 | ~5,200 kg/cm² | Designations 11 through 18 only |
| Grado 60 | ~6,000 kg/cm² | Cold-rolled, separate standard (NMX-B-072) |
Weldability warning
The Mexican deformed bar standard does not include weldability provisions, and standard varilla corrugada is not considered weldable. Weldable bar is covered by a separate standard (NMX-B-457-CANACERO). The US parallel is ASTM A706, the low-alloy weldable grade, versus A615, which is not specified for welding. Getting this wrong on a moment frame is a structural failure, not a paperwork problem.
Frequently asked questions
Is #4 rebar the same in Mexico and the United States?
Yes. Both are nominal 1/2 inch (12.7 mm). Sizes match through #8.
Is Mexican Grade 42 rebar equivalent to US Grade 60?
Their minimum yield strengths are broadly comparable — roughly 4,200 kg/cm² versus 60,000 psi — but they are governed by different standards and are not automatically interchangeable in specification.
What is the heaviest standard rebar?
In the US system, #18 at 13.6 lb/ft with a 2.257-inch nominal diameter.
Can rebar be welded?
Only bar specified as weldable. ASTM A706 in the US and NMX-B-457-CANACERO in Mexico. Standard deformed bar is not considered weldable.
How do I convert a US rebar size to metric?
Multiply the designation by 3.175 mm for sizes #3 through #8. Above #8, use the published nominal diameter rather than the number.
Sources: ASTM International, ONNCCE (NMX-C-407), CANACERO (NMX-B-506, NMX-B-457, NMX-B-072).