Why do knots weaken rope?

Knots create sharp bends in the rope where the load is not distributed evenly across all the fibres. The outer fibres at the bend carry more load than the inner ones, causing the rope to fail at a lower force than its straight-pull rated strength. Tighter bends (smaller radius) cause more strength reduction.

Which knot retains the most strength?

The double fisherman's knot retains approximately 80% of rope strength, making it one of the strongest climbing knots. The figure-eight knot retains about 75%, which is why it is the standard tie-in knot for climbing. The overhand knot retains only about 65%.

Does rope age affect knot strength?

Yes, rope fibres degrade over time from UV exposure, abrasion, and repeated loading cycles. A rope that is 3-5 years old may retain only 70-85% of its original strength even before a knot is tied. Always retire ropes according to manufacturer guidelines.

CampCalcs

Knot Strength Calculator

Compare knot types and calculate retained rope strength after tying. See how different knots affect your rope's rated strength.

Rope Rated Strength

Check rope specifications

Knot Type

Rope Material

Rope Age

How We Calculate This

This calculator applies knot efficiency factors to your rope's rated strength to show retained strength.

Knot efficiency formula

Effective strength = Rope strength x Knot efficiency x Age factor

Typical knot efficiencies

Figure-eight: ~75% retained
Bowline: ~70% retained
Double fisherman's: ~80% retained
Overhand: ~65% retained
Clove hitch: ~60% retained

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates. Always verify conditions and use proper safety equipment outdoors.