rigging

A Rope With a Knot With an 80% Efficiency Only Retains What Fraction of Nominal Strength? (2026)

A Rope With a Knot With an 80% Efficiency Only Retains What Fraction of Nominal Strength? A rope with a knot rated at 80% efficiency retains 80% of the rope's nominal (unknotted) strength — it loses 20% to the knot. So a rope rated at 5,000 lbf breaking strength holds only about 4,000 lbf once you tie an 80%-efficiency knot like a well-dressed figure-eight. Knot efficiency is the percentage of a rope's original breaking strength that survives the sharp internal bends of the knot, and "80% efficiency" is just shorthand for "keeps 80%, sacrifices 20%." Run your own rope through the Knot Strength Calculator(/tools/knot-strength-calculator) to see the exact effective strength and working load. Across roughly 108 real UseCalcPro Knot Strength Calculator sessions, the typical user checks a 10 mm rope rated 5,000 lbf with a 5:1 safety factor — and that median setup is exactly why the 80% question matters....