Formula & Calculator
Steel Reinforcement (Rebar) Weight
Estimates the weight of a steel reinforcement bar from its diameter and length, using the standard rebar weight formula.
Interpretation
Steel rebar weight: W = (D² / 162) × L, where D is diameter in mm and L is length in metres (kg). Example: 12 mm bar, L=10 m → W = (144/162)×10 ≈ 8.89 kg.
Variables
| Symbol | Quantity | Unit |
|---|---|---|
| W | Rebar weight | kg |
| D | Bar diameter | mm |
| L | Bar length | m |
What it means
The weight of steel reinforcement bars (rebars) can be estimated using the formula W = (D² / 162) × L, where D is the nominal diameter in millimetres and L is the length in metres. The constant 162 is derived from the density of steel (7850 kg/m³) and the area of a circle: weight per metre = (π D²/4) × 7850 / 10⁶ ≈ D²/162. This empirical formula is widely used in construction for ordering rebar, estimating total steel tonnage, and calculating transportation weights. It applies to standard mild steel rebars of various grades. The formula is convenient because it avoids calculating cross‑sectional area. It is also used for high‑strength bars, though density may vary slightly. Accurate weight calculation is important for structural design, cost estimation, and to ensure that the required reinforcement is available on site. This formula is a must‑know for civil engineers and quantity surveyors.
Worked example
Rebar Weight – Two Examples
Real‑World| Parameter | Value |
|---|---|
| D | 12 mm |
| L | 6 m |
| Parameter | Value |
|---|---|
| D | 16 mm |
| L | 12 m |
Common mistakes
- Diameter D: In millimetres – if using inches, convert first.
- Length L: In metres – the formula yields kg.
- Constant 162: This constant is derived from the density of steel (7850 kg/m³) and unit conversions. For different steel grades, it may vary slightly.
- Unit weight: The formula gives weight in kg. To get tonnes, divide by 1000.
- Reinforcement bending: If bars are bent, the length increases – use the actual cut length, not the straight length.
Applications
Steel rebar weight is estimated using the formula W = (D²/162) × L, where D is the bar diameter in mm and L is the length in metres, yielding the weight in kilograms. This simplified formula is widely used in construction for ordering and handling reinforcement bars. Rebars are essential for providing tensile strength to concrete structures. Structural engineers, quantity surveyors, and site engineers use this calculation to prepare bar bending schedules, to estimate total steel tonnage, and to procure materials. The constant 162 is derived from the density of mild steel and unit conversions. Accurate weight estimation ensures that enough steel is delivered to site, avoiding project delays and ensuring structural integrity.
- Preparation of bar bending schedules
- Ordering and procurement of reinforcement steel
- Cost estimation for reinforced concrete works
- Site inventory management and handling of steel bars
- Design of reinforced concrete elements (beams, columns, slabs)
Frequently Asked Questions
The weight of a rebar is W = (D² / 162) × L, where D is the diameter in millimetres, L is the length in metres, and the weight is in kilograms. This formula is for mild steel with density 7850 kg/m³.
- Using the wrong constant – the constant 162 is specific to SI units (mm, m, kg). For imperial (inches, feet, lb), use a different constant.
- Using the wrong unit for diameter – the formula expects diameter in mm; using inches gives a huge error.
- Forgetting the length – weight per metre is D²/162; multiply by the total length.
- Not accounting for overhang and bends – add extra length for laps, hooks, and bends.
For diameter in inches and length in feet, weight (lb) = (D² / 9) × L (approx). The exact formula is W = (D² × L) / 3.4 (using inches and feet). However, the metric formula is more common.
Weight per metre = 12² / 162 = 144 / 162 ≈ 0.889 kg/m. So a 12 m length weighs about 10.67 kg.
Determine the total length of each diameter from the bar bending schedule. Multiply each length by the corresponding weight per metre, sum them up. Add 5‑10% for wastage and overlaps.
The density is 7850 kg/m³ (or 0.00785 kg/cm³). The constant 162 is derived from this density and the geometric relationship for a bar.
Laps and hooks add extra length. Typically, add 10‑15% to the total straight length to account for these. The exact amount is specified in the structural drawings.
Weight = Length × Width × Thickness × Density. For steel, density ≈ 7850 kg/m³. This is used for plates, not rebar.
Divide by 1000. For example, 2450 kg = 2.45 tonnes.
Common diameters (mm): 8, 10, 12, 16, 20, 25, 32, 40. Each has a different weight per metre, which can be looked up from tables.