The thickness of a rope is indicative of a few things, namely: weight, durability, and handling. A thinner rope tends to be lighter, less durable, and better handling. For this reason, thin ropes are often chosen for hard routes where weight matters. On the other hand, a thick rope is often used in situations where the rock is more abrasive. Some people will even have two ropes – a thick one that they can fall on repeatedly without wearing it out too much and a thin one that they save for send attempts.
Single ropes typically range from 8.9mm to 11mm. For a good, all-round rope that will take a bit of a beating without being overly burdensome, look at something between 9.4 and 9.7. Anything above 10 is great as a workhorse rope that can cop some abuse, while anything below 9.4 should probably be reserved for hard send attempts as it will wear out very quickly if you spend a lot of time “hang-dogging”.
Having said all that, it’s not always the case that a thin rope is lighter than a thick rope. If you’re buying a rope for the purpose of hard sending, or you want a light rope for other reasons, make sure you check the actual weight rather than just assuming that thinner = lighter.
The length of the rope depends on where you are climbing. 40m is a standard length for an indoor gym rope, while ropes for outdoor crags tend to start at 60m with 70m and 80m ropes becoming increasingly common. Having a longer rope opens up your options for what you can and can’t climb, but if most of the climbs in your area are only 25m long there is little point buying an 80m rope as it will just make your pack heavier.
In Queensland, 60m is long enough for the majority of crags but 70m is a common choice that will make climbing inter-state and overseas less troublesome. Outside of the super-long routes in Europe, it’s very rare to require a rope longer than 70m. If you’re unsure what rope to get, the best bet is to look up the length of the routes in the areas that you will be spending most of your time.
The treatment that a rope undergoes during production impacts its durability and handling. Dry-treated ropes are better at resisting water and dirt, which increases their longevity. The treatment also means that the sheath is smoother, which leads to less friction - reducing rope drag and prolonging the life of the rope.
It’s very convenient to have a prominent marking to show the middle of the rope and most modern ropes have one of two systems for doing this. Some ropes simply have an obvious 10-15cm long marking where the middle of the rope is, while others use the "bi-pattern" method, which separates the rope into two patterns and the pattern switches at the halfway point. The first method is prone to wear and the marking can become less visible over time, while the second method should be obvious for the whole life of the rope.
It’s important that, should you ever trim your rope, you either modify the halfway point or make sure that you trim equally on both ends.
There are quite a few factors to be considered when buying a new rope. It's important to think about what features you really need your new rope to have before making a purchase. And make sure you're getting a dynamic rope not a static one!