Rebar Weight Calculation Formula (d²/162 vs ×0.00617)

The Rebar Weight Calculation Formula — Two Versions, One Answer

Engineers and quantity surveyors use two algebraically equivalent forms of the rebar weight formula. Both give the same result; the difference is notation:

• Form 1 (multiply): W (kg/m) = d² × 0.00617 — where d is bar diameter in millimetres.
• Form 2 (divide): W (kg/m) = d² / 162.2 — using the same d in millimetres.

They are identical: 1 / 162.2 = 0.006165… ≈ 0.00617. The “divide by 162” shorthand is popular in some markets and textbooks because it is easier to remember as a single number; the “multiply by 0.00617” form is more common in European structural engineering and quantity surveying software.

Where Does the Constant Come From?

The constant is derived directly from the density of steel and the geometry of a circular cross-section. Steel density (ρ) = 7,850 kg/m³ (the value used in EN 1991-1-1 and DIN 1055-1 for structural steel and reinforcing steel).

Cross-sectional area of a bar: A = π/4 × d² (in mm²). Converting to m²: A = π/4 × d² × 10⁻⁶ m².

Mass per metre: W = ρ × A = 7,850 × (π/4 × d² × 10⁻⁶) = 7,850 × π/4 × 10⁻⁶ × d².

Computing the constant: 7,850 × π/4 × 10⁻⁶ = 7,850 × 0.7854 × 10⁻⁶ = 6,165 × 10⁻⁶ = 0.006165. Rounded to 0.00617 for practical use. The divisor form: 1/0.006165 = 162.2, typically shortened to 162.

So both formulas are nothing more than the density of steel × area of a circle, expressed in convenient units for a d in millimetres and a result in kg per metre.

Reference Table — Standard DIN 488 Diameters

The values below are computed from the exact formula (density 7,850 kg/m³, circular section). The “nominal” weight per metre in EN 10080 / DIN 488 allows a tolerance of ±4.5% on the actual unit mass relative to the nominal value shown here.

Section area = π/4 × d². kg/m = d² × 0.00617 (rounded to 3 decimal places). For contract quantities always use Mill Test Certificate data.

Worked Examples

Example 1 — Single bar weight

A 20 mm B500B bar, 9.5 m cut length. Weight = 9.5 × 20² × 0.00617 = 9.5 × 400 × 0.00617 = 9.5 × 2.468 = 23.45 kg.

Example 2 — Total order tonnage from a cutting list

From your rebar cutting list: 340 bars of 16 mm at 3.2 m cut length + 180 bars of 25 mm at 7.6 m cut length.

• 16 mm: 340 × 3.2 × 256 × 0.00617 = 340 × 3.2 × 1.580 = 1,718.9 kg
• 25 mm: 180 × 7.6 × 625 × 0.00617 = 180 × 7.6 × 3.856 = 5,276.9 kg
• Sub-total: 6,995.8 kg → add 4% wastage → order 7.28 t

Example 3 — Checking a supplier quote

A supplier quotes 28.4 t for 800 pcs of 32 mm × 12 m bar. Expected: 800 × 12 × 6.313 = 60,604 kg = 60.6 t. The quote figure does not match — clarify whether the supplier quoted a different quantity, length, or diameter before proceeding.

Applying the Formula to Rebar Mesh and Coils

The same formula applies to welded reinforcing mesh and coil rebar — both are circular-section steel at 7,850 kg/m³. For a mesh panel, sum the total linear metres of wire in each direction (length × number of cross-wires + width × number of longitudinal wires) and multiply by the kg/m for the wire diameter. For coil, the coil mass printed on the label is the net steel mass; verify it matches cut-length calculations before placing the order.

Tolerance on Unit Mass per EN 10080 / DIN 488

EN 10080 §7.3 and DIN 488-1 permit a tolerance on the actual unit mass of the delivered bar of ±4.5% relative to the nominal value. In practice, mills typically aim for the positive side of this tolerance (slightly heavier than nominal) — which means your order may arrive slightly heavier than the calculated nominal mass. When comparing quote prices on a per-tonne basis, confirm whether the supplier is quoting nominal or actual mass.