Rebar Size Chart — #3 to #18 Diameter, Area & Weight
Complete rebar size and cross-sectional area reference for US imperial bars (#3–#18), Canadian/Australian metric bars (10M–55M), and quick development length values per ACI 318-19.
Imperial Rebar Sizes — #3 through #18 (ASTM A615/A706)
| Bar No. | Diameter (in) | Area (in²) | Weight (lb/ft) | Metric Approx. |
|---|---|---|---|---|
| #3 | 0.375 | 0.11 | 0.376 | 10M |
| #4 | 0.500 | 0.20 | 0.668 | 15M |
| #5 | 0.625 | 0.31 | 1.043 | 15M (similar) |
| #6 | 0.750 | 0.44 | 1.502 | 20M |
| #7 | 0.875 | 0.60 | 2.044 | 20M (similar) |
| #8 | 1.000 | 0.79 | 2.670 | 25M |
| #9 | 1.128 | 1.00 | 3.400 | 30M |
| #10 | 1.270 | 1.27 | 4.303 | 30M (similar) |
| #11 | 1.410 | 1.56 | 5.313 | 35M |
| #14 | 1.693 | 2.25 | 7.650 | 45M |
| #18 | 2.257 | 4.00 | 13.600 | 55M |
Notes on US bar numbering:
- #3 through #8: bar number = diameter in eighths of an inch (#5 = 5/8" = 0.625")
- #9, #10, #11: originally designated as 1", 1-1/8", 1-1/4" square bar equivalents
- #14 and #18: equivalent areas to former 1-1/2" and 2" square bars; rarely stocked without advance ordering
Canadian & Australian Metric Bar Sizes (10M–55M)
| Designation | Nominal Dia. (mm) | Area (mm²) | Area (in²) | Weight (kg/m) |
|---|---|---|---|---|
| 10M | 11.3 | 100 | 0.155 | 0.785 |
| 15M | 16.0 | 200 | 0.310 | 1.570 |
| 20M | 19.5 | 300 | 0.465 | 2.355 |
| 25M | 25.2 | 500 | 0.775 | 3.925 |
| 30M | 29.9 | 700 | 1.085 | 5.495 |
| 35M | 35.7 | 1000 | 1.550 | 7.850 |
| 45M | 43.7 | 1500 | 2.325 | 11.775 |
| 55M | 56.4 | 2500 | 3.875 | 19.625 |
Notes on metric bars:
- Canadian bars per CSA G30.18; Australian bars per AS/NZS 4671
- The "M" designation refers to the nominal area in units of 100 mm² (15M = 200 mm²) — not to the diameter
- Grade 500N (fy = 500 MPa) is standard in Australia; Grade 400R and 500R are common in Canada
- 15M and 20M are the most commonly stocked sizes in Canadian and Australian practice
European Metric Bar Sizes (EN 10080)
| Diameter (mm) | Area (mm²) | Weight (kg/m) | Common 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 |
European standard grade B500B: fy = 500 MPa, fu ≥ 540 MPa (k = fu/fy ≥ 1.08).
Development Length Formula (ACI 318-19)
Development length is the minimum bar embedment needed to transfer the bar's full yield force into the concrete via bond stress. Per ACI 318-19 Section 25.5.2:
ld = (3/40) × (fy / (lambda × sqrt(f'c))) × (ψt × ψe × ψs / cb + Ktr)/db × db
Simplified for the most common case (bottom bar, uncoated, normal-weight concrete, no transverse reinforcement):
ld = (fy × ψt × ψe × ψs) / (20 × lambda × sqrt(f'c)) × db
Where:
- fy = bar yield strength (psi)
- lambda = 1.0 for normal-weight concrete (0.75 for lightweight)
- ψt = 1.3 for top bars (more than 12" of concrete below); 1.0 for bottom bars
- ψe = 1.5 for epoxy-coated bars with cover < 3db; 1.0 for uncoated
- ψs = 0.8 for #6 and smaller bars; 1.0 for #7 and larger
- db = bar diameter (in)
- f'c = concrete compressive strength (psi)
Quick Development Length Table
Values in inches. Assumes: bottom bar (ψt = 1.0), uncoated (ψe = 1.0), normal-weight concrete, adequate cover (cb + Ktr)/db = 1.5 per ACI 318-19 simplified method.
| Bar | db (in) | Grade 60, f'c = 4000 psi | Grade 60, f'c = 5000 psi | Grade 80, f'c = 4000 psi |
|---|---|---|---|---|
| #4 | 0.500 | 19" | 17" | 25" |
| #5 | 0.625 | 24" | 21" | 31" |
| #6 | 0.750 | 28" | 25" | 38" |
| #7 | 0.875 | 41" | 37" | 55" |
| #8 | 1.000 | 47" | 42" | 63" |
| #9 | 1.128 | 53" | 47" | 71" |
| #11 | 1.410 | 66" | 59" | 88" |
Note: #7 and larger bars use ψs = 1.0; #6 and smaller use ψs = 0.8. This is why development length jumps between #6 and #7. Minimum ld per ACI 318-19 = 12 inches regardless of calculation.
For top bars (more than 12" of concrete below): multiply table values by 1.3.
Standard Hook Development Length
Where straight development length is impractical, standard hooks (ACI 318-19 Section 25.4.3) provide an alternative. For deformed bars with a standard 90° hook, the basic development length:
ldh = (0.02 × ψe × fy) / (lambda × sqrt(f'c)) × db
Approximate values (Grade 60, f'c = 4000 psi, uncoated, normal-weight):
| Bar | ldh (in) |
|---|---|
| #4 | 9.5" |
| #5 | 11.9" |
| #6 | 14.2" |
| #8 | 19.0" |
| #11 | 26.5" |
Minimum ldh = 8db or 6", whichever is greater. Hooks require a tail extension and specific bend radius per ACI 318-19 Table 25.3.1.
Rebar in Steel-to-Concrete Connections
Rebar appears in base plate and anchor bolt design as supplementary reinforcement:
- Hairpin bars looped around anchor bolts increase concrete breakout capacity in shear (ACI 318-19 Section 17.7.2.9)
- Ties around the anchor group provide supplementary reinforcement that can increase breakout capacity in tension
- When supplementary reinforcement is present and properly developed past the failure plane, ACI 318-19 allows phi = 0.75 (instead of 0.70 for breakout)
Frequently Asked Questions
What is the most common rebar size in US construction? #4 and #5 bars are the most commonly specified in slabs, beams, and columns. #4 (area = 0.20 in²) is standard for slab temperature and shrinkage steel; #5 (area = 0.31 in²) is common for beams and wall reinforcement.
What is the cross-sectional area of a #5 rebar? A #5 bar has a nominal diameter of 0.625" and a cross-sectional area of 0.31 in² (200 mm²). This is one of the most frequently needed values in ACI 318 flexural and shear design.
Why does rebar bar numbering skip from #11 to #14 and #18? Bar numbers #3 through #11 correspond to diameter in eighths of an inch. #14 and #18 are special bars derived from old 1-1/2" and 2" square bars, giving equivalent round bar diameters of 1.693" and 2.257". These are heavy bars used primarily in large columns and heavily loaded footings.
What rebar grade should I use? Grade 60 (fy = 60 ksi / 420 MPa) is the standard for most structural applications in the US. Grade 80 and Grade 100 are increasingly used for columns and seismic applications where higher strength reduces congestion. Always confirm the grade specified in the structural drawings.
How do I convert US rebar sizes to metric (mm) bars? There is no exact correspondence. A #5 bar (15.9 mm diameter) is close to a European 16 mm bar, and a #6 (19.1 mm) is close to a 19 mm bar. For cross-code work, compare actual diameters and areas rather than designation numbers.
Run This Calculation
→ Rebar Calculator — rebar area, spacing, and temperature/shrinkage steel requirements for slabs, beams, and walls.
→ Concrete Footing Calculator — spread footing flexural design using the bar sizes and areas from this chart.
Related Calculators
- Section Properties Calculator — for composite sections with rebar
- Base Plate & Anchors Calculator — anchor bolt design with supplementary rebar
- Rebar Development Length — ACI 318-19 ld, ldc, Hook
- Rebar Spacing Chart — ACI 318 Min & Max Spacing
- Rebar Size Reference — detailed guide on bar designation systems
- Concrete Spread Footing Design — ACI 318
- Anchor Bolt Embedment Depth — ACI 318 Chapter 17
- metric (mm, mm^2, kg/m) and imperial (in, in^2, lb/ft)
- Reference Tables Directory
- Concrete beam-column calculator
Educational use only. Development lengths depend on project-specific cover, spacing, and confinement. Always verify per ACI 318-19 or the governing concrete code with a qualified engineer.
Disclaimer (educational use only)
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