Skip to main content
Calcimator

Belay Braking Force Calculator

Calculate the braking and holding forces for different belay devices based on rope diameter, climber weight, and fall factor. Compare tubular, assisted-braking, and figure-8 devices.

Inputs

mm
lb

Results

Braking Force

1.95 kN

Belayer Holding Force

0.84 kN

Device TypeTubular (ATC)
Impact Force on Climber2.79 kN
Device Efficiency70%
How to Use This Calculator
  1. Select your belay device type: tubular (ATC-style), assisted-braking (Grigri), or figure-8.
  2. Enter the rope diameter in mm (typically 9.2–10.5 mm for a single rope).
  3. Input the fall factor for the scenario you are evaluating (use the Fall Factor calculator if needed).
  4. Read Braking Force in kN — the force the belay device can apply to arrest a fall.
  5. Check Holding Force to confirm it stays within safe limits for your belay station and anchor.
  6. Review Device Efficiency (%) to understand how much of the rope's friction is being utilized.

How the result changes with Climber Weight

Climber WeightBraking ForceBelayer Holding Force
421.33 kN0.57 kN
721.9 kN0.81 kN
1082.52 kN1.08 kN
1383 kN1.29 kN

What each input means

Belay Device Type
Select your belay device: 0 = Tubular/ATC, 1 = Assisted Braking (GriGri), 2 = Figure-8 descender.
Rope Diameter
Diameter of your climbing rope in millimeters. Thicker ropes (10-11mm) generate more friction; thin ropes (8.5-9.5mm) generate less.
Climber Weight
Body weight of the lead climber in kilograms. Heavier climbers generate higher impact forces in a fall.
Fall Factor
Expected fall factor (fall distance / rope paid out). Typical sport climbing falls are 0.3-0.7. Factor 2 is the theoretical maximum.

What each result means

Device Type
The belay device type used in this calculation.
Braking Force
Force applied to the rope by the belay device to arrest the fall.
Belayer Holding Force
Force the belayer must personally hold. Lower values mean the device is doing more work.
Impact Force on Climber
Estimated peak force experienced by the falling climber.
Device Efficiency
Percentage of impact force handled by the belay device friction.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Belay Device Type = 0, Rope Diameter = 9.8, Climber Weight = 75, Fall Factor = 0.5 = 4 input(s) provided
  2. Calculate Braking Force
    Braking Force = round((braking / 1000) * 100) / 100
    1.95 = 1.95
  3. Calculate Belayer Holding Force
    Belayer Holding Force
    0.84 = 0.84
  4. Calculate Device Type
    Tubular (ATC) = Tubular (ATC)
  5. Calculate Impact Force on Climber
    Impact Force on Climber
    2.79 = 2.79

Engine last updated . Checked against 1 independently-derived test — how we verify calculators.

Related Calculators

The questions that sit next to this one — chosen by subject, including calculators filed under a different category.

Climbing & Mountaineering

Fall Factor Calculator

Calculate the fall factor from fall distance and rope paid out. Estimate impact force and severity rating to understand climbing fall dynamics.

Climbing & Mountaineering

Rope Length Calculator

Calculate the minimum rope length needed for a climbing route based on wall height, anchor setback, knot allowance, and safety margin. Includes rappel length and recommended standard rope size.

Climbing & Mountaineering

Route Grade Converter

Convert climbing route grades between YDS, French, UIAA, British, and V-scale systems. Instantly translate difficulty ratings across international grading standards.

More in Sports, Outdoors & Recreation.