Rebar Size Chart — #3 to #18 Diameter, Area, Weight per Foot
Reinforcing steel (rebar) is specified by bar number in US practice per ASTM A615/A706. Each bar number corresponds to a nominal diameter, cross-sectional area, weight per foot, and perimeter. This page provides the complete rebar size table #3 through #18 with design values for ACI 318 flexural, shear, and development length calculations.
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Complete Rebar Size Table — #3 to #18 (ASTM A615/A706)
| Bar No. | Diameter (in) | Area (in²) | Perimeter (in) | Weight (lb/ft) | Diameter (mm) | Area (mm²) |
|---|---|---|---|---|---|---|
| #3 | 0.375 | 0.11 | 1.178 | 0.376 | 9.5 | 71 |
| #4 | 0.500 | 0.20 | 1.571 | 0.668 | 12.7 | 129 |
| #5 | 0.625 | 0.31 | 1.963 | 1.043 | 15.9 | 200 |
| #6 | 0.750 | 0.44 | 2.356 | 1.502 | 19.1 | 284 |
| #7 | 0.875 | 0.60 | 2.749 | 2.044 | 22.2 | 387 |
| #8 | 1.000 | 0.79 | 3.142 | 2.670 | 25.4 | 510 |
| #9 | 1.128 | 1.00 | 3.544 | 3.400 | 28.7 | 645 |
| #10 | 1.270 | 1.27 | 3.990 | 4.303 | 32.3 | 819 |
| #11 | 1.410 | 1.56 | 4.430 | 5.313 | 35.8 | 1,006 |
| #14 | 1.693 | 2.25 | 5.320 | 7.650 | 43.0 | 1,452 |
| #18 | 2.257 | 4.00 | 7.090 | 13.600 | 57.3 | 2,581 |
How bar numbers work: #3 through #8 correspond to the bar diameter in eighths of an inch (#4 = 4/8 = 1/2 in). #9, #10, #11 derive from old square-bar equivalents (1 in, 1-1/8 in, 1-1/4 in squares). #14 and #18 derive from 1-1/2 in and 2 in square bars.
Most Commonly Used Sizes
| Size | Primary Application | Stock Status |
|---|---|---|
| #3 | Stirrups, ties, light slabs | Readily available |
| #4 | Slabs, walls, temperature/shrinkage | Readily available |
| #5 | Beams, columns, footings | Readily available |
| #6 | Heavy beams, pile caps | Readily available |
| #8 | Columns, heavy footings | Readily available |
| #9 | Large columns, transfer beams | Special order |
| #11 | Large columns, bridge caps | Special order |
| #14–#18 | Heavy civil, very large columns | Limited availability |
Grade Markings per ASTM A615
Rebar grades are identified by rolled-in markings on the bar surface:
| Grade | Yield Strength (ksi) | Tensile Strength (ksi) | Marking | Color Code |
|---|---|---|---|---|
| Grade 40 | 40 | 60 | None (plain) | None |
| Grade 60 | 60 | 90 | One line | None |
| Grade 75 | 75 | 100 | One line | None |
| Grade 80 | 80 | 100 | Two lines | None |
| Grade 100 | 100 | 120 | Three lines | None |
The grade marking consists of continuous longitudinal line(s) on the bar surface. Grade 60 (Fy = 60 ksi / 420 MPa) is the default for most US structural applications.
ASTM A706 (Low-Alloy Weldable Rebar)
ASTM A706 is specified when welding rebar or for seismic special moment frames:
| Property | A706 Grade 60 | A615 Grade 60 |
|---|---|---|
| Minimum Fy | 60 ksi | 60 ksi |
| Maximum Fy | 78 ksi | None |
| Fy/Fu Ratio | ≤ 0.85 | ≤ 0.89 |
| Carbon Equivalent | ≤ 0.55% | Not specified |
| Weldability | Designed for welding | Not guaranteed |
A706 is mandatory for welded rebar connections in ACI 318 Section 25.5.7. Use A706 when design requires rebar welding or when seismic ductility demands controlled yield properties.
Metric Rebar Equivalents
Canadian/Australian Bars (CSA G30.18 / AS/NZS 4671)
| Designation | Dia. (mm) | Area (mm²) | Mass (kg/m) | Closest US Bar |
|---|---|---|---|---|
| 10M | 11.3 | 100 | 0.785 | #3 |
| 15M | 16.0 | 200 | 1.570 | #5 |
| 20M | 19.5 | 300 | 2.355 | #6 |
| 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 |
European Bars (EN 10080)
| Diameter (mm) | Area (mm²) | Mass (kg/m) | Grade |
|---|---|---|---|
| 8 | 50.3 | 0.395 | B500B |
| 10 | 78.5 | 0.617 | B500B |
| 12 | 113.1 | 0.888 | B500B |
| 16 | 201.1 | 1.578 | B500B |
| 20 | 314.2 | 2.466 | B500B |
| 25 | 490.9 | 3.853 | B500B/C |
| 32 | 804.2 | 6.313 | B500B/C |
| 40 | 1256.6 | 9.865 | B500C |
Development Length per ACI 318-19
The development length ld is the minimum bar embedment needed to transfer full yield force into concrete:
ld = (3/40) × (fy / (λ√f'c)) × (ψt × ψe × ψs / ((cb + Ktr)/db)) × db
Simplified Straight Development Length — Grade 60 (inches)
For bottom bars, uncoated, normal-weight concrete, with (cb+Ktr)/db = 1.5:
| Bar | f'c = 3,000 psi | f'c = 4,000 psi | f'c = 5,000 psi | f'c = 6,000 psi |
|---|---|---|---|---|
| #3 | 16 | 14 | 12 | 11 |
| #4 | 21 | 19 | 17 | 15 |
| #5 | 27 | 24 | 21 | 19 |
| #6 | 32 | 28 | 25 | 23 |
| #7 | 47 | 41 | 37 | 34 |
| #8 | 54 | 47 | 42 | 38 |
| #9 | 61 | 53 | 47 | 43 |
| #10 | 69 | 59 | 53 | 48 |
| #11 | 76 | 66 | 59 | 54 |
| #14 | 92 | 80 | 71 | 65 |
Values use ψs = 0.8 for #6 and smaller, ψs = 1.0 for #7 and larger. Minimum ld = 12 in per ACI 318-19 Section 25.4.2. For top bars (more than 12 in of concrete below), multiply by 1.3.
Rebar Area Calculation for Flexural Design
The area of steel required in flexure per ACI 318-19:
As = Mu / (φ × fy × (d - a/2))
Where a = As × fy / (0.85 × f'c × b). Common rebar combinations:
| Bar Size | Number of Bars | Total Area (in²) |
|---|---|---|
| #4 | 2 | 0.40 |
| #4 | 4 | 0.80 |
| #5 | 2 | 0.62 |
| #5 | 4 | 1.24 |
| #5 | 6 | 1.86 |
| #6 | 4 | 1.76 |
| #6 | 6 | 2.64 |
| #7 | 4 | 2.40 |
| #7 | 6 | 3.60 |
| #8 | 4 | 3.16 |
| #8 | 6 | 4.74 |
| #9 | 4 | 4.00 |
| #9 | 6 | 6.00 |
| #10 | 4 | 5.08 |
| #11 | 4 | 6.24 |
| #11 | 6 | 9.36 |
Minimum flexural reinforcement (ACI 318-19 Section 9.6.1):
As,min = 3 × √f'c × bw × d / fy (but not less than 200 × bw × d / fy)
For a 12-in wide beam with d = 20 in, f'c = 4,000 psi, fy = 60,000 psi:
As,min = 3 × √4000 × 12 × 20 / 60000 = 0.76 in²
200 × 12 × 20 / 60000 = 0.80 in² (governs)
This requires 2-#6 bars (As = 0.88 in²) or 3-#5 bars (As = 0.93 in²).
Rebar Weight Estimation
For material takeoffs and cost estimation:
| Bar | lb/ft | ft/ton | Tons per 1000 ft |
|---|---|---|---|
| #3 | 0.376 | 5,319 | 0.188 |
| #4 | 0.668 | 2,994 | 0.334 |
| #5 | 1.043 | 1,918 | 0.522 |
| #6 | 1.502 | 1,332 | 0.751 |
| #7 | 2.044 | 978 | 1.022 |
| #8 | 2.670 | 749 | 1.335 |
| #9 | 3.400 | 588 | 1.700 |
| #10 | 4.303 | 465 | 2.152 |
| #11 | 5.313 | 376 | 2.657 |
| #14 | 7.650 | 261 | 3.825 |
| #18 | 13.600 | 147 | 6.800 |
Installed rebar cost typically ranges $0.80–$1.50 per pound depending on bar size (larger bars are cheaper per pound) and project complexity.
Frequently Asked Questions
What is the cross-sectional area of a #5 rebar? A #5 bar has a nominal diameter of 0.625 in and a cross-sectional area of 0.31 in² (200 mm²). It is the most commonly used bar size for beams and general reinforcement in US construction.
What is the most common rebar size? #4 (0.500 in diameter, 0.20 in² area) for slabs and walls, #5 (0.625 in, 0.31 in²) for beams and footings, and #8 (1.000 in, 0.79 in²) for columns are the most commonly specified sizes.
What does the # in rebar sizing mean? The bar number (#3 through #8) corresponds to the diameter in eighths of an inch. A #4 bar is 4/8 = 1/2 in diameter. For #9, #10, #11, the numbers reference old square-bar equivalents. The area in in² equals the bar number divided by 10 for #3–#8 (e.g., #5 = 0.31 in² ≈ 5/16 = 0.3125).
What is the difference between ASTM A615 and A706 rebar? A615 is the standard specification for carbon-steel rebar. A706 is a low-alloy steel with controlled yield (60–78 ksi), maximum Fy/Fu ratio (≤0.85), and carbon equivalent limits, making it suitable for welding and seismic applications. A706 is required for welded rebar splices per ACI 318 Section 25.5.7.
How long is the development length for a #8 bar in 4000 psi concrete? For a bottom bar, uncoated, normal-weight concrete at f'c = 4,000 psi: ld = 47 in (approximately 4 ft). For a top bar (more than 12 in of concrete below), multiply by 1.3: ld = 61 in. Minimum ld = 12 in.
Related Pages
- Rebar Spacing Chart — ACI 318 Min & Max Spacing
- Rebar Development Length — ACI 318-19
- Concrete Footing Design — ACI 318
- Anchor Bolt Embedment Depth
- Base Plate & Anchors Calculator
- Steel Fy & Fu Table
- Section Properties Calculator
Educational reference only. Development lengths depend on project-specific cover, spacing, and confinement. Always verify per ACI 318-19 or governing concrete code with a qualified engineer.