Calculate weight for solid and open steel sections: round bar, square bar, flat bar/plate, hex bar, and angle iron. Results show kg/m, total kg, and pounds.
💡
Steel Weight by Section Type and Dimensions
BrainyCalculators editorial insight — unique to this tool
Mild steel density 7,850 kg/m³ — 12 mm TMT bar 12 m standard weighs ~10.65 kg/bar (0.888 kg/m per IS 1786). Fabricators quote by ton; freight and crane capacity need accurate tonnage from bar count.
When to use this calculator
Use for steel bar, plate, or section weight. For hollow pipe, use Pipe Weight.
Reference
Value
Context
Steel density
7,850 kg/m³
Mild steel
12 mm TMT
0.888 kg/m
IS standard
12 m bar (12 mm)
~10.65 kg
Per piece
US rebar #4
0.668 lb/ft
½ inch
Calculating hollow pipe or tube weight?
This page covers solid bars, plates, hex bars, and angle iron. For OD, wall thickness, pipe schedule, and material-density comparisons, use the
Pipe Weight Calculator →
Area = π/4 × D²
Area = S²
Area = W × T
Area = (√3 / 2) × AF²
Area = (A + B − T) × T
Weight / Metre
—
kg/m
Total Weight
—
kg
Total Weight
—
lbs
—
What is a Steel Section Weight Calculator?
A steel weight calculator estimates the mass of solid and open steel sections from cross-sectional geometry, length, and standard steel density (typically 7,850 kg/m³). This page covers round bar, square bar, flat bar or plate, hex bar, and angle iron.
Use this tool for fabrication takeoffs, construction estimates, material ordering, cutting lists, and transport planning when the member is a solid bar, plate, or angle. Each shape uses its own area formula before multiplying by length and density.
For hollow circular pipe, tube, or process piping where outer diameter and wall thickness define the section, use the Pipe Weight Calculator. Pipe weight uses OD² - ID² geometry and may involve steel, aluminium, copper, PVC, or custom density.
Section Area Formulas
Round bar: A = π/4 × D² | W = A × L × ρ / 1,000,000
Square bar: A = S²
Flat bar: A = W × T
Hex bar: A = (√3 / 2) × AF²
Angle iron: A = (A + B − T) × T
All dimensions in mm. Weight (kg) = A (mm²) × L (m) × ρ (kg/m³) / 1,000,000
How the Steel Weight Calculator Works
Formula, assumptions, and calculation steps for this engineering tool.
Methodology
Engineering calculators apply standard unit conversions and formula relationships after normalizing measurements to compatible units.
Calculation Steps
Enter dimensions, loads, rates, or electrical values.
Convert the inputs into the formula unit system.
Apply the engineering equation or conversion factor.
Return the result with units and supporting context.
Assumptions and Limits
•Material behavior is assumed ideal unless fields specify otherwise.
•Code checks, safety factors, and site conditions may require professional review.
•Use a qualified engineer for design-critical decisions.
Frequently Asked Questions
This calculator uses 7850 kg/m³ — the standard density for mild (carbon) structural steel (IS 2062, ASTM A36, S275/S355). High-strength alloy steels may vary slightly, but 7850 kg/m³ is universally accepted for structural calculations.
Mild steel has a density of 7850 kg/m³. Austenitic stainless steel (304, 316) is slightly denser at 7930–8000 kg/m³. Ferritic stainless steel is around 7750 kg/m³. For most practical engineering, the difference is less than 2% and mild steel density is commonly used as an approximation.
A quick rule of thumb for mild steel round bars: Weight (kg/m) ≈ D² / 162.2, where D is the diameter in mm. For example, a 20 mm round bar weighs about 400 / 162.2 ≈ 2.47 kg/m. This shortcut is derived from the full formula and is widely used in construction.
TMT (Thermo-Mechanically Treated) bars are reinforcement bars used in concrete structures. They are round bars with surface ribs. Their weight is calculated the same way as plain round bars using nominal diameter. Common sizes are 8, 10, 12, 16, 20, 25 and 32 mm.
A 1m × 1m steel plate weighs: Thickness (mm) × 7.85 kg. For example, a 10 mm thick steel plate weighs 10 × 7.85 = 78.5 kg per square metre. This is a handy rule: 1 mm thickness of steel weighs 7.85 kg/m².
Real-World Applications
🏗️
Structural Steel Procurement & Estimating
Structural engineers and quantity surveyors calculate the total tonnage of steel sections required for a building frame — beams, columns, bracing, and connections — to produce a Bill of Materials for procurement. Steel is priced by the tonne, so accurate weight calculation directly determines material cost. A typical multi-storey commercial building may use 30–60 kg of structural steel per square metre of floor area.
🚢
Marine & Shipbuilding Weight Budgets
Naval architects and ship designers calculate the lightship weight of a vessel — the weight of the empty ship including structure, machinery, and fittings — as the foundation of stability analysis, load capacity calculation, and freeboard determination. Steel is the dominant structural material in commercial shipping, and even small errors in weight estimation compound across thousands of structural components to produce significant displacement errors.
🛤️
Rail Infrastructure Design
Rail engineers specify steel section weights for bridge girders, station canopies, overhead line equipment masts, and track components. Railway bridges must carry defined live loads (train weights) plus their own self-weight (dead load) — steel weight calculation is fundamental to verifying that the structure's capacity exceeds the design loads with appropriate safety factors.
🔩
Fabrication Shop Scheduling & Pricing
Steel fabricators quote projects by calculating the weight of all steel sections to be cut, drilled, welded, and painted — applying a per-tonne fabrication rate plus material cost. The steel weight calculator is a daily tool in fabrication estimating, producing take-offs from design drawings to generate cost proposals for structural steelwork packages.
🚛
Transport & Logistics Planning
Long-length steel sections (6–12 metre beams and columns) must be transported from the mill or fabricator to site — logistics planning requires accurate weight calculation to assess whether a standard flatbed truck can carry a given load, whether abnormal load permits are required, and whether crane lift capacity is sufficient for the heaviest individual members.
🏭
Industrial Equipment & Machine Frames
Machine builders and industrial equipment designers calculate the self-weight of fabricated steel frames and bases for CNC machines, conveyor systems, press equipment, and storage racking — verifying that the floor loading capacity of the factory building is not exceeded and that the machine's centre of gravity is within acceptable bounds for stability during operation.
Common Mistakes
1
Using the wrong density for different steel alloys
Carbon structural steel (the most common grade — S275, S355, A36) has a density of approximately 7,850 kg/m³. Stainless steel (304, 316) is slightly denser at 7,900–8,000 kg/m³; alloy steels and tool steels can vary from 7,700–8,100 kg/m³. Using carbon steel density for stainless steel weight calculations introduces a 1–2% error — small for most applications, but significant in aerospace or precision engineering where every kilogram is optimised.
2
Confusing outside dimensions with inside dimensions for hollow sections
Hollow sections (SHS, RHS, CHS) have an outside dimension and a wall thickness — the cross-sectional area used for weight calculation is the total area minus the hollow interior area. Using the outside dimensions only (treating the section as solid) dramatically overstates the weight. Similarly, the catalogue weight-per-metre for standard hollow sections already accounts for the hollow interior — do not re-subtract the hole.
3
Not including weld metal and connection plate weights in total steel weight
Fabricated steel structures include more than just the main members — connection plates, gussets, cleats, stiffeners, end plates, and weld metal collectively add 5–15% to the weight of the basic section members. For procurement and structural analysis, this "secondary steel" must be estimated and added to the main member weight. Using member weights alone consistently underestimates total steel tonnage and procurement cost.
4
Measuring length along the centroidal axis rather than the overall member length
For curved or angled members, the length used in weight calculation should be the actual material length (along the outer face or overall envelope), not the chord length between end points. A curved beam spanning 5 metres but bent to a 10-metre arc length weighs twice as much as the straight-line distance suggests. In practice, cut lengths for procurement are always the actual material length.
5
Forgetting to convert units consistently (mm to m, kg to tonnes)
Steel section dimensions are typically given in millimetres (mm), while density is in kg/m³ and length in metres. A common error is substituting millimetre dimensions directly into formulas expecting metres — producing weight results that are 10⁶ times too large (m³ versus mm³). Always convert all dimensions to consistent SI units (metres) before calculating volume, then multiply by density in kg/m³ to get weight in kilograms.
Steel Alloy Density Quick Reference
Steel Type
Density (kg/m³)
Common Grades
Carbon structural steel
7,850
S275, S355, A36, A572
Stainless steel (austenitic)
7,900–8,000
304, 316, 321
Stainless steel (ferritic)
7,700–7,750
430, 439
Tool steel / alloy steel
7,700–8,100
H13, D2, 4140
Cast iron (grey)
7,000–7,300
GJL-250, GG25
References
Steel Construction Institute. Steel Designers' Manual. Wiley-Blackwell, 2011.
AISC. Steel Construction Manual. AISC, 2017.
EN 10034. Structural Steel I and H Sections. European Committee for Standardization, 1993.
Gere, J.M. and Goodno, B.J. Mechanics of Materials. Cengage, 2012.
Baddoo, N. Stainless Steel in Construction. Steel Construction Institute, 2014.
