About the calculator

This calculator estimates the peak forces generated during a steep traverse fall, where a climber swings (pendulums) on a rope that may be redirected through an intermediate anchor. It models both the initial arrest on the intermediate anchor and a worst-case secondary fall if that anchor were to fail at peak load, calculating the resulting forces on the intermediate anchor and the top anchor before and after failure.

The calculations are based on energy balance and rope stretch, using a simplified, conservative model calibrated to typical modern dynamic climbing ropes (single and half ropes). Rope behaviour is represented using a calibrated compliance parameter derived from published UIAA impact-force testing. The model assumes a fixed top anchor, no belayer movement, no rope cutting, and no deformation of ice or snow. Friction at the intermediate anchor can be varied to represent free-running or high-friction conditions, and optional initial slack can be included.

The results should be interpreted as order-of-magnitude peak force estimates, not precise predictions of any single real-world fall. Real outcomes depend strongly on rope condition, belay device behaviour, climber motion, and anchor quality. The calculator is intended to support comparative understanding — for example, how rope type, anchor placement, friction, or the presence or absence of an intermediate anchor affects peak loads — rather than to define absolute safety limits.

 

Using your own rope

You can choose to calculate a custom rope stiffness parameter K for a specific rope. This calculator uses a simplified, energy-based rope model calibrated to the standard UIAA impact-force test. If your rope’s published “Impact force (single)” or “Impact force (half)” value is known (from the manufacturer’s datasheet), an approximate $K$ value can be calculated directly from that number. For single ropes, use

K ≈ 360 F²

and for half ropes used as a single strand, use

K ≈ 523 F²

where F is the published impact force in kilonewtons and $K$ is obtained in newtons. These values represent a calibrated approximation of dynamic rope compliance, not a material constant. Real falls vary with rope condition, moisture, temperature, belay configuration, and loading rate, so users are encouraged to treat custom $K$ values as approximate and, where possible, explore reasonable upper and lower bounds rather than relying on a single precise number. In general, ropes designed to produce lower impact forces will stretch more, and also produce lower peak loads on anchors.

© Elke Braun-Elwert, Alpine Recreation 2025