Rebar Weight Equation
The standard empirical formula used to estimate the weight of mild steel reinforcement per meter length is based on the density of steel (approx. 7850 kg/m³).
Where:
- W = Weight in kilograms per meter length
- D = Diameter of the rebar in millimeters
Frequently Asked Questions
For metric steel rebar, the weight per meter is commonly calculated using the formula D_squared / 162.28, where D is the diameter in mm.
Rebar (reinforcing bar) is deformed steel bar embedded in concrete to provide tensile strength. Plain concrete is strong in compression (20–50 MPa) but weak in tension (only ~2–5 MPa). Rebar absorbs tensile and shear stresses that would crack unreinforced concrete. Steel and concrete are also thermally compatible (similar thermal expansion coefficients), preventing stress cracking from temperature changes.
Imperial rebar sizes (bar # = diameter in eighths of an inch): #3 (9.5mm, 0.56 kg/m), #4 (12.7mm, 0.994 kg/m), #5 (15.9mm, 1.552 kg/m), #6 (19.1mm, 2.235 kg/m), #8 (25.4mm, 3.973 kg/m). Metric rebar (European/international): 8mm (0.395 kg/m), 10mm (0.617 kg/m), 12mm (0.888 kg/m), 16mm (1.578 kg/m), 20mm (2.466 kg/m), 25mm (3.854 kg/m), 32mm (6.313 kg/m).
Minimum spacing ≥ 1.5× bar diameter or 25mm (to allow concrete to flow between bars). Maximum spacing per ACI 318 for structural slabs: 3× slab thickness or 450mm, whichever is smaller. For temperature and shrinkage reinforcement: 5× slab thickness or 450mm. Example: 150mm slab with 12mm rebar — minimum spacing = 18mm, maximum structural spacing = 450mm, typical design spacing = 150–200mm each way.
Concrete cover is the minimum distance from rebar outer surface to the nearest concrete face. It prevents corrosion and provides fire resistance. ACI 318 minimum cover requirements: Cast-in-place concrete not exposed to weather — 20mm (slabs and walls), 40mm (beams/columns); Exposed to weather (bars ≤16mm) — 40mm; Exposed to weather (bars >16mm) — 50mm; Cast against and permanently in contact with ground — 75mm. Eurocode 2 specifies cover by exposure class and design life.
Lap splice length is the overlap required when joining two rebar segments to transfer tensile forces through the concrete bond. Per ACI 318: minimum lap splice for Class B tension splices = 1.3 × development length (ld). Development length depends on bar size, concrete strength (f'c), steel yield strength (fy), and cover. Typical values: 12mm bar in 25 MPa concrete — ld ≈ 350–500mm; 20mm bar — ld ≈ 600–800mm. Compression splices are shorter: minimum 0.07 × fy × db but not less than 300mm.