Plan messenger wire spans with reliable sag estimates. Compare tension, clearance, and loading values instantly. Build safer overhead supports using clear results and graphs.
Parabolic sag approximation: S = (w × L²) ÷ (8 × H)
Required horizontal tension: H = (w × L²) ÷ (8 × S)
Support tension: T = √[H² + (w × L ÷ 2)²]
Approximate wire length: Length ≈ L + [8 × S² ÷ (3 × L)]
Clearance check: Midspan Clearance = Attachment Height − Sag
This calculator uses a common parabolic approximation for equal support elevations and uniformly distributed loading. It is useful for planning and screening checks. Final design should be verified against project codes, exact conductor properties, and site conditions.
These examples use metric inputs and the same parabolic method shown above.
| Span (m) | Unit Weight (N/m) | Load Factor | Horizontal Tension (N) | Sag (m) | Support Tension (N) |
|---|---|---|---|---|---|
| 30.00 | 12.00 | 1.00 | 4000.00 | 0.34 | 4004.05 |
| 45.00 | 15.00 | 1.20 | 6000.00 | 0.76 | 6013.66 |
| 60.00 | 20.00 | 1.15 | 9000.00 | 1.15 | 9026.41 |
Messenger wire sag is the vertical drop between the support level and the lowest point of the wire. It affects clearance, loading, appearance, and support demand across the span.
Use the load factor when your construction check must account for extra loading, such as hardware, weather effects, or conservative planning allowances. A higher factor increases sag and support demand.
Horizontal tension acts along the span. Support tension combines that horizontal force with the vertical load reaction at the support. Support tension is usually slightly larger than horizontal tension.
Attachment height lets the tool estimate midspan clearance. This helps you compare calculated sag against the minimum required space above ground, equipment, or nearby features.
This page assumes equal support elevations for quick screening. Unequal support heights change the lowest point location and the exact profile, so a detailed engineering check is recommended.
When you enter breaking strength, the calculator divides it by support tension. This gives a simple screening ratio, not a full code compliance check or final structural approval.
The graph uses a parabolic approximation, which is common for planning and short-span checks. It is usually adequate for quick estimating, but not a substitute for final detailed analysis.
You can reduce sag by increasing tension, reducing effective loading, shortening the span, or raising the support attachment point. Any change should be verified against project limits.
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.