Rebar Size Chart: Diameters, Areas and Weights
A US rebar number equals the bar diameter in eighths of an inch, so a #4 bar is 4/8, which is 1/2 inch, and a #8 is a full 1 inch. The chart below lists every standard size from #3 to #18 with its diameter, cross-sectional area and weight per foot, all set by ASTM A615. Here is how to read it, the soft metric equivalents, and a quick way to turn it into pounds of steel for your job.
Key takeaways
- The US rebar number is the diameter in eighths of an inch: #4 = 1/2 in, #5 = 5/8 in, #8 = 1 in.
- ASTM A615 covers 11 standard sizes from #3 (3/8 in) to #18 (2.257 in); residential work uses #3 to #5.
- #4 rebar weighs 0.668 lb/ft and #5 weighs 1.043 lb/ft, regardless of grade (40, 60 or 80).
- A 20 ft stick of #4 costs roughly $11 to $17; epoxy coating or Grade 60 adds 30 to 40% to the price.
How the rebar number system works
The US rebar size number is the bar diameter measured in eighths of an inch. Divide the number by 8 and you get the nominal diameter in inches. A #3 is 3/8 inch, a #4 is 4/8 which reduces to 1/2 inch, and a #8 is 8/8, a full inch.
This neat pattern holds cleanly from #3 through #8. Above that, sizes #9, #10 and #11 trace back to old square-bar equivalents, so their diameters do not land on tidy fractions. The #18 bar breaks the rule most: it is 2.257 inches, the round equivalent of an old 2 and 1/4 inch square bar.
Full US rebar size chart: #3 to #18
This is the complete ASTM A615 chart of inch-pound bar sizes. Cross-sectional area drives how much load a bar carries, and weight per foot is what you order and pay by. Notice the area in square inches roughly tracks the number over 10 for the small sizes: a #5 is about 0.31, a #6 about 0.44.
| Bar size | Diameter (in) | Area (in²) | Weight (lb/ft) |
|---|---|---|---|
| #3 | 0.375 | 0.11 | 0.376 |
| #4 | 0.500 | 0.20 | 0.668 |
| #5 | 0.625 | 0.31 | 1.043 |
| #6 | 0.750 | 0.44 | 1.502 |
| #7 | 0.875 | 0.60 | 2.044 |
| #8 | 1.000 | 0.79 | 2.670 |
| #9 | 1.128 | 1.00 | 3.400 |
| #10 | 1.270 | 1.27 | 4.303 |
| #11 | 1.410 | 1.56 | 5.313 |
| #14 | 1.693 | 2.25 | 7.650 |
| #18 | 2.257 | 4.00 | 13.600 |
To turn a bar count into total weight, multiply the weight per foot by the length of each bar and the number of bars. For a full slab grid, that means tracking every run in both directions plus overlaps and waste.
Soft metric rebar sizes explained
Almost all rebar rolled in the United States today carries a soft metric label as well as the inch-pound number. Soft metric is just a renaming: the physical bar is identical, only the size designation changes. A #4 bar is also stamped #13, and a #5 is #16.
| Imperial | Soft metric | Diameter (mm) | Weight (kg/m) |
|---|---|---|---|
| #3 | #10 | 9.5 | 0.561 |
| #4 | #13 | 12.7 | 0.996 |
| #5 | #16 | 15.9 | 1.556 |
| #6 | #19 | 19.1 | 2.240 |
| #8 | #25 | 25.4 | 3.973 |
Do not confuse soft metric with the Canadian hard metric system, where bars are labeled 10M, 15M, 20M and so on. That number is the approximate area in square millimeters, not the diameter, so a 10M bar is actually 11.3 mm across, not 10 mm.
Which rebar size for which job
For most residential concrete you will reach for #3, #4 or #5. A #3 ties into thin slabs, sidewalks and small footings. A #4 is the workhorse for driveways, patios and standard footings. A #5 steps up for heavier loads like retaining walls and structural slabs.
Commercial and industrial work routinely runs #6 through #11 in columns, beams and thick foundations. The giant #14 and #18 bars show up in bridge piers and heavy civil work, where they are usually mechanically spliced rather than lap spliced because of their size.
Once you know the bar size and spacing your plans call for, plug the slab dimensions into the rebar calculator to get the bar count, total length and weight.
To size the concrete pour itself, pair those results with the concrete slab calculator, which takes the same slab dimensions and returns volume in cubic yards or bags.
Rebar cost by size in 2026
Plain carbon steel rebar runs roughly $0.40 to $1.25 per linear foot in early 2026, with price climbing as diameter grows. A #4 bar, the most common residential size, sits around $0.55 to $0.85 per foot, so a standard 20 foot stick lands near $11 to $17 before tax.
| Size | Per foot | Per 20 ft stick |
|---|---|---|
| #3 (3/8") | $0.40 to $0.65 | $8 to $13 |
| #4 (1/2") | $0.55 to $0.85 | $11 to $17 |
| #5 (5/8") | $0.75 to $1.25 | $15 to $25 |
Two things drive the bill up. Grade 60 costs up to 40% more than Grade 40, and epoxy-coated or galvanized rebar adds 30 to 50%. Buying full 20 or 40 foot lengths and cutting on site beats paying $1.50 to $3.00 per cut at the yard. Stainless rebar is a different league, running up to $9 per foot.
Turn the chart into pounds of steel
The chart gives you weight per foot, so total steel is simple: weight per foot times the total length of bar in your layout. If a slab needs 600 feet of #4 rebar, that is 600 times 0.668, or about 401 pounds before waste.
Total weight (lb) = weight per foot × total bar length (ft)Counting bar length by hand on a grid is where mistakes creep in, especially with lap splices and edge clearance. Enter your slab size and bar spacing in the rebar calculator and it returns the bar count, total length and weight in one step.
Frequently asked questions
Is #5 or #4 rebar bigger?
What are the standard sizes of rebar?
Which is thicker, #3 or #4 rebar?
Is 1/2 inch rebar really 1/2 inch?
How much does a stick of rebar weigh?
References
- Rebar (Wikipedia)
- ASTM A615 standard specification
- Metrication of Reinforcing Steel (NPCA)
- ACI 318 Building Code Requirements