Calculator Inputs
Formula Used
Here, S is span, d is sag, L is cable length, α is thermal expansion coefficient, and ΔT is temperature change. The parabolic approximation is widely used for moderate sag conditions and quick field planning.
How to Use This Calculator
- Select a calculation mode that matches your available site data.
- Choose meters or feet for all displayed values.
- Enter span and then provide sag, cable length, or slack percent.
- Adjust thermal, elastic, and installation allowances if needed.
- Press the calculate button to view results, graph, CSV export, and PDF export.
Example Data Table
| Case | Mode | Span | Primary Input | Material | Corrected Length | Total Slack | Corrected Sag |
|---|---|---|---|---|---|---|---|
| Run 01 | Span + Sag | 20.00 m | 0.40 m sag | Steel | 20.0914 m | 0.0914 m | 0.8279 m |
| Run 02 | Span + Length | 35.00 m | 35.12 m length | Aluminum | 35.2926 m | 0.2926 m | 1.9593 m |
| Run 03 | Span + Percent | 50.00 m | 1.50 % slack | Copper | 50.8855 m | 0.8855 m | 4.0746 m |
| Run 04 | Span + Sag | 80.00 m | 1.20 m sag | Stainless Steel | 80.2413 m | 0.2413 m | 2.6906 m |
Frequently Asked Questions
1. What does cable slack mean here?
Cable slack is the extra cable length beyond the straight span between supports. It lets the line hang safely, absorb changes, and avoid over-tension during installation or temperature shifts.
2. Which mode should I select?
Use span and sag when field sag is known. Use span and cable length when the installed cable length is measured. Use slack percent when planning allowances from project standards or early estimates.
3. Why does temperature matter?
Temperature changes alter cable length through thermal expansion or contraction. A warmer line usually gets longer, increasing slack and sag. A colder line can shorten and reduce slack.
4. Is the formula exact for every cable system?
No. This tool uses a parabolic approximation, which is practical for quick planning and moderate sag. Highly loaded systems, long spans, or precision engineering checks may require catenary analysis.
5. What is elastic stretch allowance?
Elastic stretch is an optional percentage that represents added length from loading effects or expected extension. It helps planners include a small adjustment without building a full structural model.
6. Why is corrected sag larger than base sag?
Corrected sag uses the length after thermal, elastic, and installation adjustments. If those changes add cable length, the line hangs deeper, so the corrected sag becomes larger than the base sag.
7. Can I use feet instead of meters?
Yes. Choose feet in the unit selector. The page will calculate and display values in feet, while also showing a secondary value in meters for quick cross-checking.
8. Should this replace an engineer’s final design check?
No. This calculator supports planning, estimating, and field review. Final designs should still consider actual loads, support conditions, codes, safety factors, and project-specific engineering requirements.