Cable Sag Calculator

Calculate the vertical sag of a suspended cable, rope, or wire under its own weight.

Cable Parameters

Span Length (ft) (ft)

Weight per Foot (lb/ft) (lb/ft)

Horizontal Tension (lb) (lb)

Sag Analysis

Enter parameters to calculate cable sag

Overview

Cable sag is the vertical distance between the highest point of a suspended cable and its lowest point. This is critical for utility lines, bridge design, and Zip lines to ensure proper clearance and tension.

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Pro Tips

Always include the weight of any ice or wind load expected in your geographic area.
Ensure the supports (poles or anchors) can withstand the horizontal tension calculated.
For very long spans or high sag-to-span ratios, a 'catenary' formula may be required for higher precision.

Fun Facts

"The parabolic formula used here is an approximation valid when the sag is less than 10% of the span."
"Temperature changes cause cables to expand or contract, significantly affecting the sag."
"Horizontal tension is constant along the entire length of the cable in this simplified model."

Formula: Sag = (Weight × Span²) / (8 × Tension)

Used with this

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