The calculation, without hidden assumptions
Estimate mass for a thin-walled cold-formed Z or zed section from its developed centerline lengths. The calculator keeps geometry-derived mass separate from manufacturer tables: bend radii, corner deductions, coatings, holes and actual formed dimensions can change delivered kg/m.
How to use this calculator
Enter web depth, both flange widths, both lip lengths and sheet thickness.
Choose mm/in and m/ft units, then enter piece length and whole-piece quantity.
Use the documented material density; 7,850 kg/m³ is the default steel value.
Optionally enter purchasing allowance, rate/kg, target mass or supplier kg/m.
For a named proprietary Z purlin, use the current manufacturer table or certificate for final procurement and structural work.
Where people use it
- •Estimate custom cold-formed Z-purlin mass before quotation.
- •Plan roof-purlin purchasing, transport and handling tonnage.
- •Convert Z-section unit mass between kg/m and lb/ft.
- •Reverse a shipment target into whole equal-length pieces.
- •Compare thin-wall geometry with a manufacturer published kg/m value.
200 × 70/70 × 20/20 × 2 mm Z section
Developed centerline length ≈ 200+70+70+20+20 = 380 mm. Ideal area ≈ 380×2 = 760 mm². At 7,850 kg/m³ this is 5.966 kg/m; a 6 m piece is about 35.80 kg and 10 pieces about 357.96 kg.
What the result does not assume
- •This is a thin-wall developed-length mass model; it does not apply bend allowance/deduction or corner-radius corrections.
- •Manufacturer Z sections may use unequal flanges/lips, formed radii, coatings, holes and tolerances that change actual mass.
- •Do not infer a proprietary section designation or structural capacity from approximate dimensions.
- •Allowance is a purchasing assumption, not a structural or fabrication factor.
- •This calculator estimates mass only; it does not determine span, load, buckling, lapping, bridging, connection or code compliance.
Frequently asked questions
How do you calculate Z purlin weight?+
For a thin-walled estimate, add the web, two flanges and two lips to get developed centerline length, multiply by thickness for approximate area, then multiply area by material density.
Why can manufacturer kg/m differ?+
Real formed sections include bend radii, corner deductions, coatings, holes and manufacturing tolerances. Use the current manufacturer table or certificate for a named section.
Does this support unequal Z flanges and lips?+
Yes. Top and bottom flange widths and lip lengths are entered independently.
Can I calculate lb/ft?+
Yes. The result includes both kg/m and lb/ft, and total mass in kilograms and pounds.
Can it reverse-solve pieces from target weight?+
Yes. Enter a target mass and it returns how many whole entered-length pieces fit within it.
Is this a structural Z-purlin design calculator?+
No. It estimates mass and procurement quantities only; use governing design standards and manufacturer section properties for structural design.
Semantic next steps
Continue the calculation
These links move to a different input, formula or project stage rather than a keyword variation of this page.
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MAXScanner keeps the formula and assumptions beside the result so you can verify the number before using it in a drawing, estimate, specification, worksheet or document. Where a supplier, manufacturer, drawing or applicable standard owns a requirement, that source remains authoritative.