Rebar Calculator

How is Rebar Weight Calculated?

Reinforcing steel bars (rebar) weight is calculated from the bar size (diameter), length, and quantity. Unit weight is derived from the steel density (7850 kg/m³) and the nominal cross-sectional area of each bar size.

Standard rebar sizes follow designation systems like D10-D32 (metric, nominal diameter in mm) or #3-#11 (imperial, diameter in eighths of an inch). The deformed surface pattern increases bond with concrete but the nominal diameter refers to the equivalent smooth bar diameter.

Accurate rebar weight estimation is critical for structural cost estimation, procurement, and verifying that delivered quantities match design requirements. Typical waste factors of 3-5% should be added for cutting, bending, and lapping losses.

Formula: Unit Weight (kg/m) = 0.00617 × d² (d in mm) Total Weight = Unit Weight × Length × Quantity Common sizes (standard nominal table values): D10 = 0.617 kg/m, D13 = 1.04 kg/m, D16 = 1.56 kg/m, D22 = 2.98 kg/m, D25 = 3.98 kg/m — for some sizes the standard table value takes precedence over the raw formula

Example Calculation

50 pieces of D16 rebar, 12m each. Unit weight (standard nominal) = 1.56 kg/m. Total length = 50 × 12 = 600m. Total weight = 600 × 1.56 = 936 kg. With 5% waste: 936 × 1.05 ≈ 983 kg ≈ 1.0 ton.

When to Use This Calculator

• Quantity surveyors preparing bar bending schedules and material takeoffs for structural concrete projects
• Procurement officers calculating total rebar tonnage for purchase orders, including waste and lapping allowances
• Structural detailers verifying that calculated rebar weights match design drawings before submitting shop drawings
• Site engineers checking delivered rebar quantities against ordered amounts to detect shortages before placing begins

Common Mistakes to Avoid

• Forgetting lap splice lengths — every splice adds 40-60 bar diameters of extra length; for D16 at 50d, each lap adds 800mm of material
• Using the wrong unit weight formula — the simplified formula w=d²/162 gives kg/m; do not confuse with imperial formulas that give lb/ft
• Not adding a waste factor — 3-5% for straight bars, 5-7% for beams with many bends, up to 10% for complex shapes; cutting waste is unavoidable
• Mixing metric and imperial bar sizes — D16 (16mm metric) is not the same as #5 (15.875mm imperial); verify which standard the design specifies

How to Interpret Results

• Total Weight is the net steel weight (unit weight × total length) — it includes no lap splices or cutting waste, so add 40-60 bar diameters of length per splice plus 3-5% waste before ordering
• Unit Weight comes from the standard deformed-bar tables built into the tool (D10 = 0.617, D16 = 1.56, D22 = 2.98, D32 = 6.31 kg/m) — use it to spot-check deliveries by weighing a measured sample bar
• Divide Total Weight by 1000 to get tonnes for purchase orders — suppliers typically price rebar per tonne, not per bar
• Use Total Length to plan stock purchasing — dividing by the mill stock length (commonly 12 m) gives the bar count and reveals cut combinations that would generate excessive offcuts
• If the result differs from the bar bending schedule by more than a few percent, look for missing lap allowances or a bar-size mix-up (e.g., D16 vs #5) before assuming the schedule is wrong

Related Standards & References

• ASTM A615/A615M — Standard Specification for Deformed and Plain Carbon-Steel Bars for Concrete Reinforcement
• KS D 3504 — Steel Bars for Concrete Reinforcement (Korean Industrial Standard, source of the metric D-series unit weights)
• ACI 318 — Building Code Requirements for Structural Concrete (development length and lap splice provisions)
• ISO 6935-2 — Steel for the reinforcement of concrete — Part 2: Ribbed bars

Frequently Asked Questions

What is the formula for rebar weight?

The simplified formula is Weight (kg/m) = d²/162, where d is the diameter in mm. This is derived from the steel density of 7850 kg/m³ and the circular cross-section area. For D16: 16²/162 = 1.580 kg/m.

How much rebar waste should I account for?

Typical waste allowances: 3% for simple straight bars, 5% for beams and columns with many bends, and up to 7-10% for complex structures with irregular shapes. Lapping (overlap) adds 40-50 times the bar diameter at each joint.