Plan layout lines and guide cords for work. Choose sizes that resist sag and snapping. Enter your loads, spans, and preferences, then calculate now.
| Scenario | Material | Load / Tension | Safety | Span | Sag limit | Typical result (diameter) |
|---|---|---|---|---|---|---|
| Pulling a light conduit draw line | Polyester | 150 kg | 5 | — | — | ≈ 3–4 mm |
| Layout string on a long wall run | UHMWPE | 25 kgf tension | 5 | 10 m | 4 mm | ≈ 1.5–2.5 mm |
| Temporary guide line with abrasion risk | Nylon (polyamide) | 300 kg | 6 | — | — | ≈ 5–7 mm |
This calculator sizes construction strings for a target working load with practical margins. It converts your load to Newtons, applies shock and service multipliers, then uses a safety factor to estimate required breaking strength. For steady pulls, shock near 1.0 is typical; for starts, stops, and snatches, 1.2–2.0 is common. Results report diameter in millimetres and strength in kN quickly.
Material strength is adjusted for real-world losses. Efficiency represents construction and load sharing, often 0.60–0.85 for general cords. Termination factor captures knots or hardware effects; a tied knot may retain 0.60–0.80, while a good splice can approach 0.90–1.00. Condition factor reduces capacity for abrasion, UV, grit, or chemicals. These factors help match site conditions without guessing “one size fits all.”
In sag mode, the calculator checks whether your available tension can hold a span within an allowable sag. Sag increases with line weight and span squared, and decreases as tension rises. Example: with a 10 m span and a 4 mm limit, a lighter, stronger fiber can meet the limit at moderate tension, while heavier cord may require higher pull or intermediate supports. Keep spans shorter where precise finish lines matter.
Stretch is estimated using elastic modulus, line area, and applied load. Longer runs and higher tension produce greater elongation, which can shift marks during layout. Use the stretch output to decide where to re-tension, add supports, or choose a stiffer material. Treat it as a planning value; product construction and pre-tension can change results. If you see large stretch, reduce tension or increase diameter.
Length, waste allowance, and unit price help standardize purchasing. Add waste for terminations, cutbacks, and re-ties; 5–15% is typical for repetitive layout work. The cost estimate supports comparing options and avoiding undersized substitutions. Always verify selection against manufacturer ratings and your site safety rules before load-bearing use. Record the chosen diameter so crews can reorder.
It is the calculated minimum diameter that meets the adjusted breaking-strength requirement after applying your safety, shock, service, and reduction factors. Round up to the nearest available product size.
Use a lower value for knots or improvised tie-offs and a higher value for splices or rated fittings. If you are unsure, start around 0.75 and refine using manufacturer guidance.
Sag depends on weight per metre and span. Denser or thicker lines weigh more and sag more at the same tension. Higher-strength, lighter fibres can meet strength needs without excessive weight.
Yes. Select the unit next to the load or tension input. The calculator converts values internally, then reports key outputs in millimetres, kilograms, and kilonewtons for easy comparison.
Increase available tension, reduce span, allow more sag, or switch to a stronger and lighter material. Adding intermediate supports often reduces sag dramatically on long layout runs.
No. Use it for estimating and planning only. For lifting or suspended loads, use rated products, current manufacturer data, and competent review under applicable standards and site rules.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.