Whether you're pricing a PEB structure, ordering rebar, or estimating a fabrication job, getting steel weight right the first time saves you from costly over-ordering or last-minute shortages. Steel is priced and sold by weight, so every calculation below converts a physical dimension into kilograms using the density of steel: 7,850 kg/m³.
1. Steel Plates
Formula: Weight (kg) = Length (m) × Width (m) × Thickness (mm) × 7.85
Example: a plate 2m long, 1m wide, 10mm thick → 2 × 1 × 10 × 7.85 = 157 kg.
2. Round Bars
Formula: Weight (kg/m) = Diameter (mm)² × 0.00617
Example: a 20mm diameter bar → 20² × 0.00617 = 2.47 kg/m. For a 6m bar, that's 14.8 kg.
3. Square Bars
Formula: Weight (kg/m) = Side (mm)² × 0.00785
Example: a 25mm square bar → 25² × 0.00785 = 4.9 kg/m.
4. Pipes (Hollow Round Sections)
Formula: Weight (kg/m) = (Outer Diameter − Wall Thickness) × Wall Thickness × 0.02466
Example: a pipe with 100mm OD and 5mm wall thickness → (100−5) × 5 × 0.02466 = 11.7 kg/m.
5. I-Beams and Channels
These use standardized weight-per-meter values published by steel manufacturers (e.g., ISMB, ISMC, or ASTM tables), since the cross-section isn't a simple rectangle. Always check the manufacturer's published kg/m rating rather than trying to calculate it from raw dimensions — the web-to-flange ratio varies by profile.
Common Mistakes to Avoid
- Forgetting to convert mm to meters consistently — mixing units is the single most common estimation error
- Using nominal (catalog) dimensions instead of actual measured dimensions for older or non-standard stock
- Ignoring cutting/wastage allowance — add 3–5% for real-world offcuts
- Assuming all steel grades have identical density — 7,850 kg/m³ is standard for mild steel/carbon steel; stainless steel is closer to 8,000 kg/m³
Skip the Manual Math
Our Steel Weight Calculator handles plates, bars, pipes, and beams instantly — just enter your dimensions and get an accurate weight in seconds, with support for multiple units.