For many climbers, purchasing a rock climbing rope is like unwrapping one of Willy Wonka’s golden tickets: It’s often the final item you need to unlock a world of adventurous outdoor routes, not to mention lead-climb in the gym whenever you please.

However, buying the best rock climbing rope to fit your needs is no small hurdle. So much of your safety depends on your rope, and there are tons of sizes, lengths, and types to choose from. Here’s what you need to know to make a smart choice buying:

1. Why diameter matters in rock climbing ropes
2. How to choose a rope length
3. What UIAA Safety Certifications mean   
4. The difference between half ropes, twin ropes, and single ropes
5. Other features to consider
6. How to choose a rock climbing rope

Why Diameter Matters in Rock Climbing Ropes

Rock-climbing ropes get their strength from a thick core made of twisted yarns, encased in a “sheath” that protects the core. Most ropes are made of the same material—nylon—which means that their strength comes not from material differences but from the thickness and density of the core. (There are some exceptions listed in the section below on UIAA safety certifications.)

Pros and Cons of Thick Ropes

Generally, the thicker the rope, the more durable it will be. However, thicker ropes—between 10 and 10.7 mm in diameter—can be a pain to drag up wandering or low-angle rock faces and may not fit in all belay devices (be sure to check manufacturer recommendations for your device before you buy a rope). Thick ropes also tend to be heavier. However, they’re a great choice for frequent top-roping, climbing in sandy terrain, and other types of climbing that can quickly wear down a rope.

Pros and Cons of Thin Ropes

On the other hand, thinner ropes—between 8.9 to 9.6 mm—encounter less friction against the rock, feel light, and can be a great choice for climbing sport routes at your limit. Their light weight can also make them a good option for alpine routes with long approaches. However, skinny ropes may be too thin for certain belay devices to grab securely—be sure to check the recommendations for your belay devices before you use them.

How to Choose a Rope Length

For most climbers, this is a simple choice between the two most widely available lengths of rock climbing rope: 60 meters and 70 meters. 60-meter ropes are less expensive and weigh less than their 70-meter counterparts. However, some longer routes require a 70-meter rope (or, less commonly, an 80-meter rope) to lower or rappel to the ground. This is usually marked clearly in guidebooks. Check the areas where you’ll be climbing most frequently to make your choice.

If you’re only looking for a gym-climbing rope, you may want to save money by going even shorter—most gyms only require a 30- or 35-meter rope. Check with your local gym first.  

What UIAA Safety Certifications Mean

When you buy a rope, you’ll see lots of technical specifications that can look like gibberish. The truth is that any rope certified by the UIAA (Union Internationale des Associations d'Alpinisme) is rigorously tested and determined safe for climbing. However, these specs can offer some clues as to how durable a rope will be and how it will feel to fall on. Here are the basics. 

Sheath Percentage: This is the proportion of the rope that is sheath. A higher percentage could indicate that the rope is more abrasion-resistant, but thicker sheaths also tend to be stiffer and harder to handle. 

Impact force: This has to do with how much force is imparted to the climber—as opposed to absorbed by the rope—during a fall. Compare several ropes. The one with the lowest impact force will be the stretchiest, and therefore the least likely to give you whiplash during a big fall.

UIAA falls: The UIAA rates each rope for a certain number of falls. However, the falls they test in the lab create more force than most actual climbing falls ever do, so this is more of a relative statistic useful for comparing one rope to another. More UIAA falls may indicate that a rope is more durable. (PSA: Always check your rope for damage after a big fall.)

Dynamic elongation: This is how much the rope stretches during its first UIAA fall test. More dynamic elongation means a “softer catch,” i.e. a less jarring fall. You want this number to be moderate—around 25 to 35 percent. If your rope is on the stretchier side, just make sure your belayer is mindful if you’re falling near the ground or a ledge.

Static elongation: Static or “working” elongation is how much the rope stretches naturally when you’re just hanging on it, as opposed to falling. You want a lower number here. 

The Difference Between Half Ropes, Twin Ropes, and Single Ropes

On the rope tag, you’ll see a marker indicating whether it is to be used as part of a single-rope or double-rope system. A circled “1” labels a single rope, a circled infinity symbol shows twin ropes, and a circled “½” indicates that it is a half rope. Half ropes and twin ropes must be used together in a two-rope system. Climbing with two ropes is popular in alpine climbing and particularly in ice climbing, where it provides redundancy if one rope gets cut or damaged by a crampon. Two-rope systems also make it easier to do full rope-length rappels without having to carry up a heavy second rope. However, even the lightest pair of twins weighs more than a light single rope, and two ropes can be complicated to manage.

Single ropes are usually between 9 and 10.5 mm in diameter. They can be used on their own, but must be doubled-over to rappel. This is the most common and popular type of rope. 

Half ropes are usually 8 to 9 mm in diameter. They must be used together and clipped through alternate pieces of gear. Some half ropes can also be used as thin single ropes. Be sure to check the tag before you buy.

Twin ropes are the skinniest, sometimes as thin as 7.0 mm. They must be clipped together into every piece of gear. Some twin ropes can also be used as half ropes—check before you buy.

Other Features to Consider

There are a few other things to look out for before you buy a rock climbing rope.

Dynamic or Static: If you’re planning to climb on your rope, make sure it’s a “dynamic rope,” which means it will stretch and absorb shock during falls. If you are simply looking for a rope to build anchors with—common in areas where anchoring features like large trees are set back from the lip of the cliff—you may want a static rope in addition to your dynamic climbing rope.

Middle Mark: Some rock climbing ropes have a section of black dye in the center to tell you where the approximate middle is. This is very useful for efficient rappelling, though the dye often fades over time. Fortunately, you can also buy special rope-safe middle-mark dye yourself if you want to add or refresh a mark later.

Bi-pattern: Bi-pattern ropes are usually striped on one side and dotted or checkered on the other. The two patterns switch halfway, making it easy to find the middle of the rope during a rappel. And unlike a middle-marked rope, the pattern won’t fade over time.

Dry treatment: Ropes are usually made of nylon, which naturally absorbs water. Since soggy nylon is much weaker than dry nylon, some rock climbing ropes are dry-treated, which means the external sheath has a waterproof coating. Others are “double-dry” treated, which means both the sheath and core are coated. Dry-treated ropes are more expensive, but the treatment extends the life of your rope by keeping out moisture and dirt and reducing friction. Dry ropes are the standard for climbing wet or icy conditions, as in mountaineering or ice climbing.

How to Choose a Rock Climbing Rope

Before you shop for a new rope, ask yourself these questions. 

Rope Diameter

1. Will I be mostly top-roping or taking big falls on sport routes? If so, will I need a thicker workhorse rope?
2. Will I be hiking long distances to reach multi-pitch objectives? Should I look for a thinner, lighter-weight rope for these goals?
3. Will I be climbing on sandy or abrasive rock that could necessitate a thicker, more durable rope, or at least a thicker sheath? 

Rope Length

1. Will I be using my rope only for gym climbing? In that case, do I need a 30-, 35-, or 40-meter rope to safely climb in my local gym?  
2. Will I be doing long rappels or lowering off long routes that might require a 70-meter or even 80-meter rope?
3. Do I plan to mostly climb at my local sport crags, in which case a 60-meter rope might be plenty sufficient?

Rope Features

1. Do I plan to use my rope for wandering terrain or ice climbing? If so, should I consider a two-rope system?
2. Will I be doing much ice climbing, snow climbing or mountaineering? If so, should I consider a dry-treated rope?
3. Will I be doing a lot of rappelling that could require a middle-marked or bi-pattern rope?

All articles are for general informational purposes.  Each individual’s needs, preferences, goals and abilities may vary.  Be sure to obtain all appropriate training, expert supervision and/or medical advice before engaging in strenuous or potentially hazardous activity.