Rebar Size Chart
Bar number to diameter, cross-sectional area, and weight per foot for standard US rebar.
| Bar # | Common size | Diameter | Cross-section area | Weight |
|---|---|---|---|---|
| #3 | 3/8 in | 0.375 in | 0.11 sq in | 0.376 lb/ft |
| #4 | 1/2 in | 0.500 in | 0.20 sq in | 0.668 lb/ft |
| #5 | 5/8 in | 0.625 in | 0.31 sq in | 1.043 lb/ft |
| #6 | 3/4 in | 0.750 in | 0.44 sq in | 1.502 lb/ft |
| #7 | 7/8 in | 0.875 in | 0.60 sq in | 2.044 lb/ft |
| #8 | 1 in | 1.000 in | 0.79 sq in | 2.670 lb/ft |
| #9 | 1-1/8 in (nominal) | 1.128 in | 1.00 sq in | 3.400 lb/ft |
| #10 | 1-1/4 in (nominal) | 1.270 in | 1.27 sq in | 4.303 lb/ft |
| #11 | 1-3/8 in (nominal) | 1.410 in | 1.56 sq in | 5.313 lb/ft |
US rebar is sized by a bar number that corresponds to its diameter in eighths of an inch -- a #4 bar is 4/8 in (0.5 in), a #6 bar is 6/8 in (0.75 in), and so on through #8. Above #8, the numbering continues but no longer maps to a clean fraction (a #9 bar is sized to have the same cross-sectional area as a 1-1/8 in square bar, not a true 9/8 in diameter).
Cross-sectional area matters for structural calculations -- it's what an engineer uses to determine a slab or footing's reinforcement capacity, not just the bar's diameter. Weight per foot is useful for estimating total rebar tonnage on a larger job.
Where these numbers come from
Standard ASTM rebar sizing (imperial, #3 through #11). Always follow your project's engineering spec or local building code for the actual size and spacing required -- this chart is a reference, not a substitute for an engineer's design.
Frequently asked questions
Why is rebar labeled #3, #4, #5 instead of a size in inches?
The bar number refers to its diameter in eighths of an inch -- a #4 bar is 4/8 in (1/2 in), a #8 bar is 8/8 in (1 full inch). It's a US rebar sizing convention, not an arbitrary label.
What's the most common rebar size for residential footings?
#4 rebar (1/2 in) is common for residential footings and slabs; #3 shows up in smaller applications like sidewalks. Always follow your specific project's engineering spec or local code, not a general rule.
Does this include metric rebar sizes?
No, this covers standard US imperial rebar sizes (#3 through #11). Metric rebar uses a different numbering system based on millimeter diameter.
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