Tree Work
Rope Load (WLL) Calculator
Pick your rope material and diameter, choose a design factor (5:1 standard, 10:1 life support), and get the safe working load and minimum breaking strength.
Safe Working Load (lb)
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- Minimum Breaking Strength (lb)
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- Rope tag class
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- Design factor used
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FAQ
Why 5:1 vs 10:1? +
ANSI Z133-2017 calls for a 5:1 design factor for rigging that holds wood, and 10:1 for any rope a climber is attached to. Lifting overhead loads where workers can pass under typically uses 15:1.
How accurate is the diameter scaling? +
Rope strength scales roughly with cross-sectional area, so MBS goes up with diameter squared. This calc uses 1/2" as the published baseline. For exact numbers, check the manufacturer spec sheet — Samson, Yale, and Sterling all publish full tables.
Why is Dyneema so much stronger? +
UHMWPE (Dyneema/Spectra) has roughly 3-4x the tensile strength of polyester at the same diameter. The tradeoff is poor heat resistance and almost no elongation, which means more shock load on the anchor.