Steel weight calculator.
Theoretical weight for round, square, flat, hexagonal and tube sections using dimensions and quantity.
Total weight
| # | Material | Qty | Kg / Piece | Exact Total | Rounded Up |
|---|
How to calculate steel weight: formula and units
Theoretical weight follows from cross-sectional area, length and material density. For one row containing identical pieces:
m = A × L × ρ × 10−9 × n
- A: cross-sectional area in mm²; L: length of one piece in mm.
- ρ: density in kg/m³; n: positive whole-number quantity; m: theoretical net weight of the row in kg.
- The “Steel” option uses 7.85 g/cm³ = 7,850 kg/m³ as its calculation density. When density is expressed in g/cm³, use 10−6 instead of 10−9.
All length fields expect millimetres: 1 m = 1,000 mm. The examples below consistently use 7,850 kg/m³. Choosing another material changes the calculation density, not the geometry.
The model assumes a constant cross-section and uniform density. Actual dimensions, manufacturing tolerances, coatings and additional machining may change the weight. These are theoretical values, not scale readings or a binding quotation.
Worked examples for five sections
These are geometric reference examples, not customer records or delivery commitments. Table net values are displayed to four decimal places; whole-kilogram rounding is applied to each unrounded row total.
| Section and area A | Inputs | Net per row | Whole kg, up |
|---|---|---|---|
| Round bar A = π × d² / 4 | Diameter d = 50 Length 1,000; 2 pieces | 30.8269 kg | 31 kg |
| Square bar A = a² | Side a = 40 Length 2,000; 3 pieces | 75.3600 kg | 76 kg |
| Flat bar A = b × t | Width b = 100; thickness t = 20 Length 1,000; 4 pieces | 62.8000 kg | 63 kg |
| Hexagonal bar A = √3 × s² / 2 | Across flats s = 50 Length 1,000; 2 pieces | 33.9915 kg | 34 kg |
| Tube A = π × (D² − dᵢ²) / 4 | Outside Ø D = 100; wall t = 10 Inside Ø dᵢ = 80; length 1,000; 2 pieces | 44.3907 kg | 45 kg |
Hexagon: s is the distance across two opposite parallel flats, not across the corners. Tube: inside diameter dᵢ = D − 2 × t. Wall thickness must be positive and smaller than half the outside diameter.
To check the round-bar example: A = π × 50² / 4 ≈ 1,963.4954 mm². With a length of 1,000 mm, density of 7,850 kg/m³ and quantity of 2, the theoretical row weight is approximately 30.8269 kg.
Net weight is not the rounded row total
The calculator first multiplies the unrounded unit weight by quantity. Only then is each row rounded up to a whole kilogram. A value that is already a whole kilogram stays unchanged. Unit weight is not rounded up before multiplication.
The five example rows give 247.3691 kg theoretical net weight and 249 kg as the sum of individually rounded rows. Rounding the net grand total only once would give 248 kg; that is not this calculator’s list rule.
One round-bar example piece weighs approximately 15.4134 kg. Two pieces weigh 30.8269 kg and therefore make a 31 kg row — not 16 × 2 = 32 kg. Display precision is limited; calculations retain the unrounded values.
Copy the list or save it as a PDF while keeping net and rounded totals separate. Machining and saw allowances are not rounding rules: see the expandable measurement guidance directly inside the calculator.
Steel weight calculator questions
How do I calculate weight per metre?
Select the section and enter its dimensions. Set length to 1,000 mm and quantity to 1. The theoretical unit weight then represents one metre of that constant cross-section.
Which dimensions do hexagonal bar and tube need?
Hexagonal bar uses the across-flats dimension. Tube uses outside diameter and wall thickness; the calculator derives the inside diameter. Outside diameter alone is not enough to determine tube weight.
Are cutting or machining allowances added automatically?
No. Only entered dimensions are calculated. Use finished dimensions for finished-part net weight. For material-consumption estimates, include confirmed allowances yourself in the appropriate dimensions. Saw kerf consumes length and is not a diameter increase.
Why can the result differ from weighed material?
The calculation uses ideal geometry and the selected density. Actual dimensions, surface condition, density and machining may differ. Use the agreed delivery and weighing conditions for actual billing, not automatically the theoretical weight.
Can I calculate several dimensions in one list?
Yes. Add each combination of section, dimensions, material and quantity as a separate row. The list shows the net total alongside the sum of rows individually rounded up to whole kilograms. Remove individual rows or clear the complete list as needed.
Which entries are invalid?
Section dimensions, length and density must be positive; quantity must be a positive whole number. Tube inside diameter must remain positive after subtracting twice the wall thickness. Blank fields, invalid numbers and non-finite results are not accepted as valid rows.
From calculated weight to a material enquiry
Weight alone does not specify steel grade or delivery condition. State the required grade, section dimensions, finished length, quantity and cutting requirements in your enquiry. A shape supported by the tool does not imply that a matching sales product is currently available.
- Detailed steel weight formulas and dimensions
- Cold-drawn transmission shaft: product information
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- Cutting and other services
- Technical information for material selection
- Enquire about material and cutting
Examples and units checked against geometric formulas and the existing calculator on 18 October 2026. Model examples do not replace material testing or project-specific engineering approval.
Steel density, specific weight and grade selection
The steel option uses 7.85 g/cm³ = 7850 kg/m³ = 0.00000785 kg/mm³. With this assumption, 1 m³ has a mass of 7850 kg; actual material density and weighed mass must be checked separately.
The result in kg is mass. In physics, weight is a force measured in N; weight per volume is measured in N/m³. This calculator returns kilograms, not force.
C45 / CK45 and transmission shafts use the same section geometry; a grade name does not determine dimensions or certified density. Check section dimensions, length, quantity and the selected density. Do not model a welded hollow section as a solid square.
C45 / CK45 product and delivery information · Transmission shaft product information
Unit meanings: NIST SI guide. This unit reference is not a density certificate for a steel grade.
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