Fall Factor Calculator
The fall factor - fall distance divided by rope length absorbing it - is the number that actually drives impact force. Enter the two distances and climber weight; the force estimate comes from a spring model calibrated to standard UIAA drop tests.
Result
- Estimated peak force on the climber
- 1,169 lbf
- Estimated rope stretch
- 17%
Spring model calibrated so the UIAA reference drop (80 kg, factor 1.77) lands near 9.9 kN, in the range of modern single ropes.
For understanding the physics, not for deciding what is safe. The model ignores belay device behavior, rope wear, knots, friction and belayer mass - real forces differ. Never base protection decisions on a calculator.
How the calculation works
The factor is one division; the force comes from treating the rope as a spring:
m·g·(d + x) = ½·K·x² ⇒ F = K·x, K = 30000 N / L
The stiffness constant K is calibrated so the UIAA 101 reference drop - 80 kg at factor 1.77 on a 2.8 m strand - lands near 9.9 kN, matching modern single ropes. From there the model scales honestly with factor, weight and rope length, but real systems bleed energy in ways it cannot see.
For understanding the physics, not for deciding what is safe. The model ignores belay device behavior, rope wear, knots, friction and belayer mass - real forces differ. Never base protection decisions on a calculator.
The full story - why factor 2 is special, what friction does, and how belaying changes the numbers - is in the fall factor guide. The receiving end of that force, the anchor, is on the anchor force calculator.
Planning estimate only - not safety advice.
Frequently asked questions
Why is fall factor more important than fall distance?
Because the rope absorbs energy in proportion to its length in play. A 4 m fall on 40 m of rope (factor 0.1) is gentle; the same 4 m fall on 4 m of rope (factor 1) is severe. Distance alone tells you almost nothing about the load on your gear.
When is a factor 2 fall actually possible?
Only when you fall from at or below the anchor with slack in the system - the classic case is falling straight down past a belay ledge with no protection below the anchor. Above the anchor, the belayer and rope in the system keep the factor below 2, which is why protecting the pitch early matters so much.
How accurate is the force estimate?
It is a calibrated spring model: it reproduces the UIAA reference drop (80 kg, factor 1.77) at about 9.9 kN, in the band where modern single ropes actually land. It ignores belay device behavior, rope slip through the belay, friction over edges, knots and rope age - all of which reduce real peak forces, sometimes a lot. Treat it as an upper-bound illustration.
What elongation number makes sense?
Dynamic ropes stretch 25-40% in a hard standard test; the model outputs similar magnitudes for big falls. High stretch means a softer catch and more fall distance traveled - both real effects your belayer experiences as a "long" catch.