Understanding CordageIndependent rope educationStart choosing
Menu

Calculator bench

The math is useful when its limits stay attached.

These tools expose inputs, units, formulas, and exclusions. They help readers understand relationships; they do not approve rope, hardware, or systems.

Interactive tool · non-life-safety only

Load & design-factor explorer

Shows arithmetic, not approval

Explore the relationship between an estimated peak load and a design factor you supply. This is not a working-load-limit generator.

Enter force in pounds-force, not mass. You are responsible for the load estimate and factor; dynamic effects can dominate the result. This page validates your entries itself rather than relying on browser pop-ups, so every rejected value gets a written reason.

Interactive tool · exact conversions

Force & length converter

Same fact in every context

Restate one force or one length in the units rope data sheets actually use. Every factor below is exact by definition, so the conversion itself adds no uncertainty — only your original measurement does.

This tool has no context gate, and that is deliberate. A conversion is the same fact in every application: 5 kN is 1,124 lbf whether the line is holding a tarp or a person. Refusing to convert would teach nothing and would train you to click past the stops that do matter.

Force

Kilograms-force (kgf) is included because readers think in kilograms, but it is a force unit, not a mass. It is converted through standard gravity — 1 kgf = 9.80665 N exactly. A 1 kg mass exerts 1 kgf only while it hangs still, or moves at steady speed, in standard Earth gravity. Accelerate it, drop it, or snatch it and the real force is larger. Kilograms read off a scale are mass; rope ratings are force.

Length

Leave either group blank to convert only the other one. Lengths here are plain geometry — this tool does not know whether the rope is loaded, and does not add stretch.

1 lbf = 4.4482216152605 N exactly1 kgf = 9.80665 N exactly (standard gravity, gₙ = 9.80665 m/s²)1 in = 25.4 mm exactly · 1 ft = 0.3048 m exactlyResults carry at least four significant figures, or more if your entry does.Defined values from NIST Special Publication 811, Appendix B.

Interactive tool · non-life-safety only

Elongation estimator

Estimates movement, not clearance

Turn an elongation percentage you have read on a manufacturer’s data sheet into approximate movement over a length you specify. Both numbers come from you. The arithmetic is length × percentage ÷ 100, and that is the entire model.

Never use this to plan fall clearance.

The distance required below a worker or a climber is a life-safety calculation that depends on the whole system — energy absorber, lanyard, anchorage height, harness, device, the specific rope model, free-fall distance, and the manufacturer’s own clearance instructions. A percentage multiplied by a length does not answer it and must not be substituted for it.

What this tool does not know

  • The load at which your percentage was measured. Elongation is a curve, not a constant — the same rope moves differently at a light load than near its rated strength.
  • Whether your figure is working elongation, elongation at a stated fraction of breaking strength, or elongation at break. Those are different claims and are not interchangeable.
  • Whether it was measured statically or dynamically. A shock or sudden arrest moves rope further than a slowly applied load.
  • Whether the rope is new, bedded-in, cycled, wet, dirty, or aged, and what knots, splices, and terminations add on top.
  • Your actual rope. This is arithmetic on a number you typed, not a substitute for the manufacturer’s elongation curve, data sheet, or instructions.

There is no default percentage here on purpose — publishing a “typical” figure for a fiber would be inventing data about a rope we have never seen. Copy the number from the data sheet for the exact product, and note the conditions printed beside it.

How to read the results

Multiplication is not a working load limit.

The load explorer’s result is the estimated load multiplied by a factor the visitor selected. It is not a manufacturer’s working load limit and does not account for the actual rope, construction, knots, splices, bends, temperature, contamination, wear, loading rate, hardware, or rules.

Never use the load explorer or the elongation estimator for climbing, fall arrest, rescue, human suspension, lifting people, overhead lifting, or an unknown shock-loaded system.

Why the digits stop where they do

A result cannot be more precise than what went into it. The load explorer rounds its headline to the significant figures your load estimate carries, and rounds up rather than down, because a required minimum should never shrink in the rounding—the exact product is printed beside it either way. The elongation estimator rounds to whichever of your two entries is less precise. The converter is the deliberate exception: its factors are exact by definition, so it reports at least four significant figures and leaves the precision of your own measurement to you.

Sharing a result

Once a tool produces a result, the address bar carries the inputs, so the page can be bookmarked or sent to someone else and it will reopen showing the same arithmetic. The intended-context selector is deliberately left out of that link: a shared address should never pre-answer the safety question for the next reader.

Read breaking strength is not a working loadfor the definitions and assumptions behind the tools.