Fall factor solver
Fall factor = fall length ÷ rope out. It — not the raw fall distance — is what determines how hard a climbing fall is.
Presets use meters. Switch units any time — values convert automatically.
- Fall length
- 4.0 m
- Rope out
- 8.0 m
Fall factor diagram
Schematic only — not to scale. The climber falls twice the distance they were above their last piece of protection.
Reading the result
- 0 – 0.3
- Low — e.g. top-rope slips and short falls on lots of rope.
- 0.3 – 1.0
- Moderate — typical lead falls with gear below you.
- 1.0 – 1.7
- High — long falls, little rope out, or high above the last piece.
- 1.7 – 2.0
- Severe — approaching a factor-2 fall, the theoretical maximum in lead climbing.
A factor-2 fall happens when a leader falls with no protection between them and the belay — e.g. falling 6 m with only 3 m of rope out. Same fall factor = same impact force, whether the fall is 2 m or 20 m.
Impact force calculator
This climbing impact force calculator estimates the peak force on the climber in a lead climbing fall, using the UIAA / Goldstone standard equation calibrated by your rope's published UIAA impact-force rating.
- UIAA single-rope limit
- 12.0 kN
- Margin to UIAA limit
- –
- Est. rope stretch
- –
The equation used
Impact force F = Wg + √((Wg)² + F₀(F₀ − 2m₀g)(m/m₀)(f/f₀)), where Wg is the climber's weight, F₀ the rope's published UIAA impact force, m₀ = 80 kg and f₀ = 1.77 the UIAA drop-test conditions. Derived from energy conservation; the rope's unknown stiffness is eliminated using the manufacturer's own UIAA test result, so the estimate is calibrated to real test data rather than a guessed modulus (Goldstone / Wikipedia "Fall factor" derivation).
Gear kN rating checker
Compare a computed impact force against a piece of climbing gear's rated strength (climbing gear strength is stamped in kN on the gear itself). Ratings below are typical values — always check the kN marking stamped on your own gear and edit the field to match.
Tip: compute a realistic force in the Impact Force tab, then send it here.
- Gear rating
- –
- Impact force
- –
- Absolute margin
- –
What kN ratings mean
Climbing gear is marked with its minimum breaking strength (MBS) in kilonewtons. 1 kN ≈ 102 kg of static weight — but a falling climber multiplies their weight many times over, which is why ratings look "huge" compared to body weight. Carabiners show three numbers: major axis (e.g. 24 kN), minor/cross-loaded axis (e.g. 8 kN) and gate-open (e.g. 9 kN) — the weakest direction governs.
Rope database — published UIAA values
Curated from manufacturers' published UIAA test data — these climbing rope safety ratings are printed on every rope label (retailer spec sheets cross-checked, Oct 2026). Specs change by model year — always verify against your own rope's label and use the Custom entry for anything not listed.
| Rope | Ø mm | Impact force F₀ | Static elong. | Dynamic elong. | UIAA falls |
|---|
Compare two ropes
Same climber, same fall — how much does dynamic rope elongation matter for the impact force?
Static vs dynamic elongation — what the numbers mean
- Static elongation
- Stretch under a steady 80 kg load (EN 892: max 10% for single ropes). What you feel hanging on the rope or top-roping — lower is less "bouncy".
- Dynamic elongation
- Stretch measured in the UIAA drop test (max 40%). Higher = softer catch but a longer fall; this is the main lever on impact force.
- UIAA falls held
- How many factor-1.77 test drops with an 80 kg mass the rope survived (EN 892 requires ≥ 5 for single ropes). A measure of durability, not a fall allowance.
Via ferrata fall factor
On a via ferrata the "rope" is your lanyard — often just ~1 m long — so fall factors can far exceed the lead-climbing maximum of 2.
EN 958 certifies via ferrata sets with an 80 kg mass dropped 5 m.
✓ Certified EN 958 energy-absorbing set
Tear-webbing absorbers rip open progressively, stretching the stop over distance. The standard limits peak force to 6 kN for an 80 kg mass in a 5 m drop — the only acceptable option on a via ferrata.
- Peak force (certified)
- ≤ 6.0 kN
- After any real fall
- retire the set
✗ Plain sling / lanyard (no absorber)
A static nylon sling barely stretches, so the energy has nowhere to go. Rough energy-model estimate for this fall:
Estimate assumes a sewn nylon sling (~22 kN at ~20% elongation); cross-checked against a published UIAA journal drop test on a sewn sling (~18 kN at factor 1.77). Never use a non-absorbing sling as a via ferrata lanyard.
Anchor & belay force estimator
How much climbing anchor force does a fall generate? The anchor doesn't just feel the climber's impact force — it feels the climber plus the belayer's side of the rope, minus friction losses.
- Scenario multiplier
- –
- Per piece (2-pc, if perfectly equalized)
- –
Where the ⁵⁄₃ comes from
When a leader falls onto a top piece, the piece holds the climber's rope tension plus the tension on the belayer's side. Friction over the carabiner dissipates roughly a third, so the conventional estimate for the top piece / anchor load is (1 + ⅔) × F = ⁵⁄₃ × F (Goldstone). Rope drag through many pieces changes the real number — another reason these are estimates.
Methodology, sources & limits
Model & sources
- Fall factor
f = fall length ÷ rope out— the standard definition used by UIAA, Petzl and AMGA teaching materials. - Impact force uses the UIAA / Goldstone "standard equation"
F = Wg + √((Wg)² + F₀(F₀ − 2m₀g)(m/m₀)(f/f₀))withm₀ = 80 kg,f₀ = 1.77(derivation: Wikipedia, "Fall factor"; R. Goldstone, "The Standard Equation for Impact Force"). The rope's unknown stiffness is eliminated via its own published UIAA test result — at the UIAA test conditions the equation returns exactly the published rating, by construction. - Rope data are manufacturers' published UIAA single-rope values, cross-checked across retailer spec sheets (Oct 2026). Specs vary by model year — the Custom entry lets you use your own rope's label values.
- Anchor multiplier ⁵⁄₃ is the conventional value for a redirected leader fall (Goldstone; friction over the top carabiner ≈ ⅓ of the leader-side tension).
- Via ferrata: EN 958 requires energy-absorbing sets to keep peak force ≤ 6 kN for an 80 kg mass in a 5 m drop. The plain-sling estimate uses a linear energy model for sewn nylon (~22 kN at ~20% elongation), cross-checked against a UIAA journal drop test on a sewn sling (~18 kN at factor 1.77).
Assumptions & limits (read before trusting any number)
- Clean rope run: no rope drag, no sharp edges, no rope-on-rope friction. Real drag raises the effective fall factor.
- Rigid test mass and linear rope response — real ropes are non-linear and hysteretic; knots, harness stretch and belayer movement all absorb energy.
- UIAA test conditions (80 kg, factor 1.77) are far more severe than most real falls; the equation extrapolates from them.
- Gear ratings are lab breaking strengths (MBS), not working loads; placement quality dominates real outcomes.
- Nothing here is safety advice. Climbing decisions belong with certified instruction and manufacturers' documentation.
A note on Petzl's retired calculator
Petzl once offered an online fall-force simulator but withdrew it; climbers on forums have noted its absence for years. This lab is an independent educational tool built on the published UIAA/Goldstone equation — not affiliated with Petzl or any rope manufacturer.