Belay Braking Force Calculator

Each device type is assigned its own base friction coefficient — 0.95 for assisted braking (GriGri-style), 0.7 for a tubular/ATC, and 0.55 for a figure-8 — reflecting how much rope friction the mechanism itself generates before your brake hand adds anything. Device Efficiency is just that effective friction expressed as a percentage, so the assisted-braking device reports the highest share of the fall arrested by the device alone, which is also why its calculated Belayer Holding Force comes out lowest.

No — there's no rope-length input at all. The impact-force model assumes a fixed nominal 5 meters of rope out and a constant rope stiffness value regardless of how much rope is actually paid out in your scenario, then scales the peak force with the Fall Factor you enter. That makes the kN figures useful for comparing devices, rope diameters, and fall factors against each other, but not a substitute for a fall calculation tied to your real rope length.

Rope diameter feeds a multiplier on the device's base friction coefficient: for every millimeter above the 9.8mm baseline, effective friction increases about 6%, and for every millimeter below it, friction decreases by the same amount. Physically this reflects a thicker rope's larger surface area creating more friction against the device's braking surfaces, which raises Braking Force and lowers Belayer Holding Force at the same fall factor.

Holding Force is what's left of the impact force after the device's own friction has done its share of the work — it's calculated as Impact Force minus Braking Force, floored at zero. A lower value means the device is absorbing more of the fall itself, so the belayer needs to supply less brake-hand force to keep the rope from slipping, which is generally considered safer and less fatiguing on long or heavy-fall sessions.