#4 Rebar (1/2 Inch Reinforcing Bar)
Authoritative dimensional properties, unit weight, cross-sectional area, spacing tables, standard hook geometries, and ACI 318-19 tension development length for structural concrete design.
| Bar Designation | #4 | Code Standard | ASTM A615 / A706 |
| Nominal Diameter (db) | 0.5 in | Metric Diameter | 12.7 mm |
| Cross-Sectional Area (Ab) | 0.2 in² | Metric Area | 129 mm² |
| Linear Weight | 0.668 lb/ft | Metric Mass | 0.994 kg/m |
| Nominal Perimeter | 1.571 in | Metric Perimeter | 39.9 mm |
| Minimum Clear Spacing | max(1.0″, 0.5″) | ACI Provision | ACI 318-19 §25.2.1 |
| Hook Type | Min. Inside Bend Pin | Extension Length (US) | Extension Length (SI) |
|---|---|---|---|
| 90° Standard Hook | 3″ (76 mm) | 6″ (12db) | 152 mm |
| 180° Standard Hook | 3″ (76 mm) | 2.5″ (max(4db, 2.5″)) | 64 mm |
Common Structural Applications
- ›The most common residential and commercial rebar size in North America
- ›Beam stirrups and column ties for standard structural members
- ›Slab-on-grade mats, basement stem walls, and footing mats
- ›Retaining wall stem reinforcement for low-to-mid heights (under 8 ft)
Standard 90° hook requires 6-inch tail (12db). 180° hook requires 2.5-inch extension. Excellent balance between stiffness and field-bendability.
#4 Rebar Spacing Table (As / Unit Width)
Area of longitudinal reinforcement provided for slabs, walls, and footing mats at given on-center spacings.
| 3″ o.c. | 4″ o.c. | 5″ o.c. | 6″ o.c. | 7″ o.c. | 8″ o.c. | 9″ o.c. | 10″ o.c. | 12″ o.c. | 14″ o.c. | 16″ o.c. | 18″ o.c. |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 0.800in²/ft | 0.600in²/ft | 0.480in²/ft | 0.400in²/ft | 0.343in²/ft | 0.300in²/ft | 0.267in²/ft | 0.240in²/ft | 0.200in²/ft | 0.171in²/ft | 0.150in²/ft | 0.133in²/ft |
ACI 318-19 Tension Development Length (ld)
Calculated using ACI 318-19 Section 25.4.2.3 simplified method for Grade 60 (420 MPa) deformed bars in normal-weight concrete with clear spacing ≥ db and clear cover ≥ db.
| Concrete Strength (f'c) | Bottom Bars (ld) [ψt = 1.0] | Top Bars (ld) [ψt = 1.3] | Governing Provision | Minimum Limit |
|---|---|---|---|---|
| 3,000 psi | 21.9″(556 mm) | 28.5″(724 mm) | ACI 318-19 Table 25.4.2.3 | ld ≥ 12″ (300 mm) |
| 4,000 psi | 19″(483 mm) | 24.7″(627 mm) | ACI 318-19 Table 25.4.2.3 | ld ≥ 12″ (300 mm) |
| 5,000 psi | 17″(432 mm) | 22.1″(561 mm) | ACI 318-19 Table 25.4.2.3 | ld ≥ 12″ (300 mm) |
| 6,000 psi | 15.5″(394 mm) | 20.1″(511 mm) | ACI 318-19 Table 25.4.2.3 | ld ≥ 12″ (300 mm) |
Design Reinforcement with #4 in AXIS
Run instant ACI 318-19 beam flexure, shear stirrup spacing, column P-M interaction, and development length checks with full KaTeX step-by-step audit logs.