Rebar Size Chart (#3 to #18)
Diameter, area and weight for every ASTM A615 bar size, plus soft metric and Canadian equivalents
Written by M., a general contractor in Richmond, VA · Last updated
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Rebar Size Chart: Quick Reference
A #4 rebar is 1/2 inch in diameter, has a cross-sectional area of 0.20 square inches, and weighs 0.668 pounds per foot. Bar sizes run from #3 (3/8 in) to #18 (2-1/4 in). Every value in this chart is the ASTM A615 nominal dimension; the bar you buy carries the same numbers regardless of grade.
| Bar size | Diameter (in) | Diameter (mm) | Area (in²) | Weight (lb/ft) | Weight (kg/m) | Soft metric |
|---|---|---|---|---|---|---|
| #3 | 0.375 | 9.5 | 0.11 | 0.376 | 0.560 | #10 |
| #4 | 0.500 | 12.7 | 0.20 | 0.668 | 0.994 | #13 |
| #5 | 0.625 | 15.9 | 0.31 | 1.043 | 1.552 | #16 |
| #6 | 0.750 | 19.1 | 0.44 | 1.502 | 2.235 | #19 |
| #7 | 0.875 | 22.2 | 0.60 | 2.044 | 3.042 | #22 |
| #8 | 1.000 | 25.4 | 0.79 | 2.670 | 3.973 | #25 |
| #9 | 1.128 | 28.7 | 1.00 | 3.400 | 5.060 | #29 |
| #10 | 1.270 | 32.3 | 1.27 | 4.303 | 6.404 | #32 |
| #11 | 1.410 | 35.8 | 1.56 | 5.313 | 7.907 | #36 |
| #14 | 1.693 | 43.0 | 2.25 | 7.650 | 11.38 | #43 |
| #18 | 2.257 | 57.3 | 4.00 | 13.60 | 20.24 | #57 |
Nominal dimensions per ASTM A615/A615M. Diameter and area are the values of a plain round bar of the same weight; the deformations (ribs) are not included. Weights match the constants used by our rebar calculator.
How Rebar Sizes Are Named
The bar number is the diameter in eighths of an inch. #3 is 3/8 in, #4 is 4/8 or 1/2 in, #8 is 8/8 or 1 in. The rule holds exactly through #8. From #9 up the numbers are approximate: a #9 bar is 1.128 in, sized so its area is 1.00 sq in, and the same logic gives #10 (1.27 sq in), #11 (1.56), #14 (2.25) and #18 (4.00). There is no #12, #13, #15, #16 or #17.
Since the 1990s, bars have been rolled with soft metric designations: the same physical bar, labeled by its diameter in millimeters. #4 is stamped 13, #5 is 16, #8 is 25. If a drawing calls for "No. 16 bar" and the yard only knows #5, they are the same steel. The chart above shows both.
| Imperial | Fraction | Soft metric | Diameter |
|---|---|---|---|
| #3 | 3/8 in | #10 | 9.5 mm |
| #4 | 1/2 in | #13 | 12.7 mm |
| #5 | 5/8 in | #16 | 15.9 mm |
| #6 | 3/4 in | #19 | 19.1 mm |
| #7 | 7/8 in | #22 | 22.2 mm |
| #8 | 1 in | #25 | 25.4 mm |
| #9 | 1-1/8 in | #29 | 28.7 mm |
| #10 | 1-1/4 in | #32 | 32.3 mm |
| #11 | 1-3/8 in | #36 | 35.8 mm |
| #14 | 1-3/4 in | #43 | 43.0 mm |
| #18 | 2-1/4 in | #57 | 57.3 mm |
Canadian Metric Bars (CSA G30.18)
Canada uses hard metric sizes designated by approximate area in square millimeters. A 10M bar (100 mm²) is close to a US #3; 15M (200 mm²) is close to #4; 20M (300 mm²) is close to #5. They are not interchangeable on a stamped drawing, but the table lets you compare.
| CSA size | Diameter (mm) | Area (mm²) | Mass (kg/m) | Closest US bar |
|---|---|---|---|---|
| 10M | 11.3 | 100 | 0.785 | #3 |
| 15M | 16.0 | 200 | 1.570 | #4 |
| 20M | 19.5 | 300 | 2.355 | #5 |
| 25M | 25.2 | 500 | 3.925 | #8 |
| 30M | 29.9 | 700 | 5.495 | #9 |
| 35M | 35.7 | 1000 | 7.850 | #11 |
| 45M | 43.7 | 1500 | 11.775 | #14 |
| 55M | 56.4 | 2500 | 19.625 | #18 |
Which Rebar Size for Which Job
Residential concrete almost always uses #3, #4 or #5. Larger bars are specified by an engineer for a reason, and substituting sizes changes both strength and spacing. When a plan is silent, these are the conventional choices:
| Bar | Diameter | Typical use |
|---|---|---|
| #3 | 3/8 in | Patios, sidewalks, 4 in slabs on grade, stirrups and ties |
| #4 | 1/2 in | Driveways, garage floors, footings (IRC R403.1.3), foundation walls, retaining walls under 4 ft |
| #5 | 5/8 in | Footings under 2-story loads, basement walls, retaining walls, grade beams |
| #6 | 3/4 in | Heavy footings, columns, engineered grade beams, tall retaining walls |
| #7 and #8 | 7/8 to 1 in | Commercial foundations, piers, structural columns and beams |
| #9 to #11 | 1-1/8 to 1-3/8 in | Bridges, high-rise columns, mat foundations |
| #14 and #18 | 1-3/4 and 2-1/4 in | Heavy civil and nuclear work; special-order only |
Spacing matters as much as size. A 4 in slab with #3 at 18 in each way and a 5 in driveway with #4 at 12 in are the common residential layouts; the rebar spacing guide covers the ACI 318 rules and the rebar calculator counts the bars.
Grade Markings and How to Read a Bar
Every deformed bar carries four rolled-in marks in order along its length: the producer's mill symbol, the bar size (4 or 13 for a #4), the steel type letter, and the grade. Grade is the minimum yield strength in ksi.
| Mark | Meaning |
|---|---|
| S | ASTM A615 carbon steel (the standard bar) |
| W | ASTM A706 low-alloy, weldable |
| R | ASTM A996 rail steel |
| A | ASTM A996 axle steel |
| No grade mark | Grade 40 (40,000 psi yield) |
| One longitudinal line or "60" | Grade 60 (60,000 psi), the default for most work |
| Two lines or "75" | Grade 75 |
| "80" or "100" | Grade 80 / Grade 100 high-strength bars |
Grade does not change weight or diameter. A Grade 60 #4 and a Grade 40 #4 weigh the same 0.668 lb/ft; the difference is how much load the bar carries before it yields.
Stock Lengths, Bends and Splices
Stock lengths
- - Home centers sell 20 ft sticks (and pre-cut 2, 3, 4 and 10 ft pieces) in #3, #4 and #5.
- - Rebar yards stock 20, 30, 40 and 60 ft and will cut and bend to a schedule.
- - A 20 ft #4 stick weighs 13.4 lb; a 20 ft #5 weighs 20.9 lb. See the rebar weight chart for every size and length.
Minimum bend diameter (ACI 318-19 Table 25.3.1)
- - #3 through #8: 6 bar diameters (a #4 bends around a 3 in pin).
- - #9, #10, #11: 8 bar diameters.
- - #14 and #18: 10 bar diameters.
- - Stirrups and ties #3 to #5: 4 bar diameters.
Lap splice length
- - Rule of thumb for Grade 60 in 3,000 psi concrete: 40 bar diameters for #3 to #6 (20 in for #4, 25 in for #5). Engineered work uses ACI 318 Chapter 25 development lengths, which run longer for top bars and epoxy-coated bars.
The rebar calculator adds lap length to every splice automatically when your run is longer than the stock length.
Frequently Asked Questions
What size is #4 rebar?
#4 rebar is 1/2 inch (12.7 mm) in nominal diameter, with a cross-sectional area of 0.20 sq in and a weight of 0.668 lb per foot. In soft metric it is labeled 13. It is the most common bar in residential driveways, footings and foundation walls.
What does the number on rebar mean?
The size number is the bar diameter in eighths of an inch: #3 is 3/8 in, #5 is 5/8 in, #8 is 1 in. Above #8 the numbers are nominal and the bars are sized by area instead (#9 has exactly 1.00 sq in). The other marks on the bar are the mill, steel type and grade.
Is #3 or #4 rebar better for a slab?
For a 4 in patio, sidewalk or shed slab, #3 at 18 in on center is standard. For a driveway, garage floor or any slab 5 in or thicker that carries vehicles, use #4 at 12 to 18 in. Larger bar in a thin slab does not help: the slab needs a minimum 1.5 in of cover, and #4 fits a 4 in slab only barely.
What is 10M rebar?
10M is the Canadian CSA G30.18 designation for a bar with a nominal area of 100 mm² and diameter of 11.3 mm, weighing 0.785 kg/m. It is the closest Canadian equivalent to a US #3 (3/8 in) bar, though slightly larger.
How much does a 20 ft stick of #4 rebar weigh?
13.4 lb (20 ft × 0.668 lb/ft). A 20 ft #3 weighs 7.5 lb, a 20 ft #5 weighs 20.9 lb and a 20 ft #6 weighs 30.0 lb. A bundle of ten 20 ft #4 sticks is 134 lb, which is why the yard loads them with a forklift.
What is the difference between Grade 40 and Grade 60 rebar?
Yield strength: Grade 40 yields at 40,000 psi and Grade 60 at 60,000 psi. They are the same size and weight for a given bar number. Grade 60 (marked with one line or "60") is the default for nearly all US construction; Grade 40 is now mostly limited to small-diameter ties and some residential work where the plan allows it.
Quick Reference
- - #3: 3/8 in · 0.11 in² · 0.376 lb/ft · soft metric 10
- - #4: 1/2 in · 0.20 in² · 0.668 lb/ft · soft metric 13
- - #5: 5/8 in · 0.31 in² · 1.043 lb/ft · soft metric 16
- - #6: 3/4 in · 0.44 in² · 1.502 lb/ft · soft metric 19
- - #8: 1 in · 0.79 in² · 2.670 lb/ft · soft metric 25
- - Size number = eighths of an inch through #8; grade never changes size or weight.