Steel Weight Calculator
Calculate the total weight of steel reinforcement bars (rebar) given their diameter, length, and quantity. Ideal for quantity surveyors and site engineers preparing bar bending schedules and material orders.
About this calculator
The weight of a mild steel or deformed reinforcement bar is derived from its volume and the density of steel (≈ 7,850 kg/m³). For a circular bar, volume per metre = π/4 × d², and multiplying by density gives a weight per metre of approximately d²/162 kg/m, where d is in millimetres. This is the industry-standard shortcut formula: Weight (kg) = (d² / 162) × L × n, where d = diameter in mm, L = length in metres, and n = number of bars. The constant 162 comes from 4 × density in kg/mm²·m units, rounded for practical use. The formula gives results accurate to within ±1% for standard Fe415 and Fe500 rebar used in reinforced concrete construction.
How to use
You need to find the weight of 20 bars of 16 mm diameter rebar, each 6 m long. Using the formula: Weight = (d² / 162) × L × n = (16² / 162) × 6 × 20. Step 1: 16² = 256. Step 2: 256 / 162 = 1.580 kg/m. Step 3: 1.580 × 6 = 9.481 kg per bar. Step 4: 9.481 × 20 = 189.6 kg total. This matches the standard weight table value of 1.58 kg/m for 16 mm bar. You would order approximately 190 kg, adding 3–5% for laps and wastage.
Frequently asked questions
Why is the constant 162 used in the steel rebar weight formula?
The constant 162 is derived from the density of steel and the geometry of a circular cross-section. Steel density is approximately 7,850 kg/m³. For a bar of diameter d mm, weight per metre = (π/4) × (d/1000)² × 7,850. Simplifying: (π × 7,850) / (4 × 1,000,000) ≈ 1/162. Rounding π × 7,850 / 4 = 6,162 to 6,000 and expressing per 1,000,000 gives the 1/162 shortcut. The approximation is accurate enough for site quantity estimation but may differ by ~0.5% from precise calculations.
How do I calculate rebar weight for different bar sizes and lengths on a BBS?
A Bar Bending Schedule (BBS) lists each bar mark with its diameter, shape code, cutting length, and quantity. For each bar mark, apply Weight = (d² / 162) × L × n and sum all entries. Cutting length must include allowances for hooks and bends — a standard 180° hook adds approximately 9d to the bar length. After totalling all bar marks, add 3–5% for laps, chair bars, and site wastage before raising a purchase order.
What is the weight per metre of common rebar sizes used in construction?
Using the d²/162 formula: 8 mm bar ≈ 0.395 kg/m, 10 mm ≈ 0.617 kg/m, 12 mm ≈ 0.888 kg/m, 16 mm ≈ 1.580 kg/m, 20 mm ≈ 2.469 kg/m, 25 mm ≈ 3.858 kg/m, and 32 mm ≈ 6.321 kg/m. These values match IS 1786 and BS 4449 published tables. Knowing these unit weights allows quick mental checks on site without a calculator — for instance, a tonne of 12 mm bar gives roughly 1,126 metres of rebar.