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Fall factor equals fall distance divided by rope length paid out (between climber and belayer). UIAA requires single ropes to hold Factor 1.77 test falls. Lower factor means less energy per unit rope.
FF = Fall distance / Rope out (max theoretical = 2.0)UIAA specifies maximum 40% dynamic elongation for single ropes in factor 1.77 tests. Actual stretch in field falls depends on fall factor, rope age, and wetness. Typical lead fall stretch: 10–30% of rope out.
Stretch ≈ Rope out × Dynamic elongation % × FF adjustmentPeak impact force (kN) depends on fall energy, rope stretch, and friction in the system. UIAA max for single ropes: 12 kN. Lighter climbers and higher fall factors increase peak force on the top piece.
Impact force ∝ (Climber weight × Fall distance) / Total stretchUpdated: July 2026
Climber falls 5m on 10m rope out: FF = 0.5. On a new 9.5mm rope with ~30% dynamic elongation, expect ~1.5m rope stretch plus belayer displacement. Moderate impact force.
Climber at 3m above bolt with 3m rope out falls 6m: FF = 1.0. High impact — rope stretches maximally, top carabiner and bolt see peak force. Soft catch technique reduces climber impact.
20m rope out, 4m fall: FF = 0.2. Low factor — minimal stretch and low impact force. Long pitches with good protection spacing produce safer low-factor falls.
Use only the rope length between climber and belayer (rope paid out), not the full 60m or 70m rope on the ground. A 60m rope with 5m out and 5m fall is factor 1.0, not 0.08.
Even new UIAA-rated ropes transmit significant force at factor 1.0+. Protection placement quality, belay technique, and climber weight matter as much as rope condition.
Dynamic climbing ropes stretch to absorb fall energy and reduce impact force on the climber and protection. Fall factor, rope diameter, and climber weight determine how much a rope elongates and the peak force transmitted. This calculator estimates stretch and impact for lead climbing falls.