How Long is My Climbing Rope?

As the Technical Advisor here at Sterling, I handle a lot of customer service questions. One that I receive quite often is:

Hey, I just measured my rope and it’s only 58 meters (188.5’).

What’s up with that?

My response is to ask, how was the rope measured? Generally, the response is some variation of laying the rope out and measuring it with a tape measure. While this seems logical, this is not an accurate way to measure rope because most materials used in making rope are somewhat elastic.

Fibers can shrink 10% or more during the rope construction process. Most rope manufacturers condition the yarns they use to build their ropes. This helps to give the yarn the elastic properties we want. It also helps limit the amount of shrinkage that occurs after construction. To expand on this, the most common material used in making kernmantle rope, nylon, is a dynamic fiber that is constantly shrinking and expanding depending on a multitude of variables including temperature, humidity, pressure, and field use. This property, while annoying, is also what makes nylon great for use in life safety ropes. It’s strong, it stretches and there is no better fiber currently available. After and during use, ropes can continue to change. A rope left in the trunk of your car may expand (not desirable in very hot, dry places); a rope in your cold cellar may contract. Don’t worry though; the reality is that when you weight your rope on rappel or take a leader fall, the rope is stretching out.

Because of the variables that affect rope length, there is a standard on how to accurately measure a rope. Please refer to (external link to PDF) Annex 2 of UIAA 101. Using this standard will give you a more accurate measurement of your rope or cord. Without going into details, this method essentially puts the rope under tension first and then measures. The rationale behind measuring a rope under tension is that you can counteract some of the variables (temperature, humidity, pressure) that may affect the individual rope fibers. In order to compensate for many of the above condition changes and to guarantee our rope lengths, Sterling cuts its ropes 3% to 5% longer than the reported length.