Trusted methodology for accurate rebar weights
This calculator applies first-principles geometry and the standard density of carbon steel to compute precise rebar weights. It supports both custom diameters and standard size series, with unit-aware conversions to ensure consistency.
Data Source and Methodology
Authoritative references:
- EN 1991-1-1:2002 (Eurocode 1), Annex A, Table A.1 — Density of materials: steel = 78.5 kN/m³ ≈ 7850 kg/m³. Link: European Commission Eurocodes. Date: 2002.
- ASTM A615/A615M-20e1 — Standard Specification for Deformed and Plain Carbon-Steel Bars for Concrete Reinforcement (US bar size system and nominal properties). Link: ASTM International. Date: 2020.
Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da questa fonte.
The Formula Explained
Cross‑sectional area of a circular bar:
A = \frac{\pi}{4}\,d^{2}
Unit weight (mass per unit length):
w = A \cdot \rho = \frac{\pi}{4}\,d^{2}\,\rho
where d is diameter in meters, \rho is steel density (kg/m³), and results in kg/m.
Common engineering shortcuts (equivalent):
w\,[\mathrm{kg/m}] \approx 0.006165 \cdot d_{\mathrm{mm}}^{2}
w\,[\mathrm{lb/ft}] \approx 0.167 \cdot \#^{2} (US bar sizes)
Glossary of Variables
- Units: Choose Metric (mm, m) or Imperial (in, ft).
- Bar Size: Standardized diameters (Metric list or US # sizes).
- Diameter: Nominal diameter for custom input.
- Length per piece: The length of each bar; selectable units.
- Quantity: Number of bars of the specified length.
- Density: Material density (default 7850 kg/m³).
- Unit weight: Weight per meter and per foot.
- Weight per piece: Unit weight multiplied by bar length.
- Total weight: Weight per piece times quantity.
- Cross-sectional area: Area of bar section (πd²/4).
- Volume per piece: Area times length.
How It Works: A Step-by-Step Example
Scenario: Metric units, 16 mm rebar, 6 m per piece, 25 pieces, density 7850 kg/m³.
- Convert diameter: d = 16 mm = 0.016 m.
- Compute area: A = (π/4)·d² = (π/4)·(0.016)² = 2.0106×10⁻⁴ m².
- Unit weight: w = A·ρ = 2.0106×10⁻⁴ × 7850 ≈ 1.579 kg/m.
- Weight per piece: 1.579 × 6 = 9.474 kg.
- Total weight: 9.474 × 25 = 236.85 kg (≈ 522.3 lb).
Frequently Asked Questions (FAQ)
Does ribbing (deformation) affect weight?
Ribbing has negligible effect on weight for estimation. Standards define nominal diameters/weights that already account for manufacturing tolerances.
Why are #9 and larger US bar diameters not multiples of 1/8 inch?
ASTM specifies nominal diameters for larger bars to meet mechanical requirements; these differ slightly from the simple #/8 rule.
Can I enter total length instead of length per piece?
Use Quantity = 1 and set Length to your total run, or split into piece length × number of bars for shop-friendly takeoffs.
How accurate is the density assumption?
7850 kg/m³ is the widely accepted nominal density for carbon steel in design codes. For stainless or special alloys, override density to refine results.
Do results include wastage or cutting allowances?
No. Add your project-specific allowance separately (e.g., 2–5%) depending on bending schedules and offcuts.
What precision should I use for purchasing?
Round up to supplier increments and include an allowance. Always validate against fabricator schedules and code-specific tolerances.