What's the Best Climbing Rope Diameter?

Rope diameter and rope length are two of the biggest decisions to make when buying a rope. Is a bigger or smaller rope diameter better? In this post we dive into where each rope diameter excels.

Dynamic climbing ropes have less than a 5 mm range, from the skinniest 6.9 mm to the widest still-made-for-climbing 11.5 mm. Today, the majority of ropes that are bought for rock climbing range from 9 mm – 10 mm, so the nuances here are small, but important.

In general smaller ropes will be lighter and more pliable, while thicker ropes can offer more durability (as they use more rope fibers), and be significantly easier to handle as there will be more friction while belaying.

10.3 MM AND ABOVE

Really only used in gyms or by rescue teams and other more professional uses.

10.1 MM – 10.2 MM

In the 2010’s, in the US, 10.2mm was THE go-to standard for a climbers first rope. It would be very rare to hear suggestions to go smaller (there are only a handful of 10.1mm options available). Today, climbers who choose this rope diameter are leading in the gym or setting up / climbing a lot of top-ropes outdoors. Other climbers will use this diameter for hauling systems (routesetting or big wall climbing). 10 – 10.2mm is still seen as the ‘most durable’ option, as they require more fibers to create the larger sheath diameter.

10.2mm is the largest diameter that will still work well in many belay devices. Since 10.2 mm is on the larger side of belay device allowance, the rope will move through the belay device slower than a smaller diameter rope. This slowness can be a good thing (if you’re looking for more control) or a bad thing (if you feel it moves too slow).

Belay Device Note: Some belay devices are certified to handle single ropes as big as 11 mm. That does not mean that diameter is for optimal use. It just means, technically, a new rope of that size could fit through. The experience could be incredibly frustrating, especially if the rope is older/fuzzier. If possible, try your friends rope, or ask the gym if they have any ropes available to test how your belay device handles different diameters.

Most gym top ropes are in the 10 – 11mm range, and especially when those ropes get fuzzy with use, it can feel like the rope barely moves through the belay device, especially if your climber is light weight. You can always ask your gym what diameter they use, and that can help decide if this diameter works for you before you buy your own rope.

Below you’ll find 10.1 – 10.2mm examples in various lengths. The shorter lengths (30 – 40m) are intended as indoor lead climbing ropes, as indoor gym walls are not as tall as many outdoor climbing areas.

9.8 MM – 10 MM

In the 2020’s, 9.8 mm – 10mm are the most common diameters for a first rope, for climbing indoors or out. It’s often considered the new standard for an all-around-do-anything “workhorse” rope that is great for single pitch climbing, sport or trad.

Manufacturers often market 9.8 – 10mm as great for projecting. It is a bit smaller than standard gym ropes, so it may feel slipperier to handle. If this is your first rope, take extra caution during first few uses.

This range often has a lower elongation rate that can be nice for tight top ropes. It’s also helpful for the belayer to belay dynamically, to help create a soft catch during a lead fall.

If a gym has ropes to rent / borrow for lead belaying, they are often in (or very close to) this diameter range.

9.8mm is by far the most commonly available diameter. 9.9mm and 10mm are harder to find, but work to bridge the gap that used to exist between 10.2 -> 9.8mm. Here are some popular examples for indoor (<50m) and outdoor (>60m):

9.5 MM – 9.7 MM

This range is most often a climbers 2nd – 5th rope. The skinnier diameter is lighter if you have a longer approach. The lightness is also noticeable on 70m-80m rope lengths.

This size assumes there is a more equal mix of leading vs top-roping (versus majority top-roping), as this diameter balances weight and durability. This same balance also makes many trad climbers lean towards this rope range. Newer alpine climbers in particular will use this rope range as a workhorse rope, leaning towards the wider side for shorter approaches / sharper rock or skinnier side for longer approaches.

You’ll find this diameter range is where the rope will noticeably feel smoother and faster – through your belay device, through bolts and protection, and through the anchor.

9.1 MM – 9.4 MM

These diameters (and smaller) are the skinniest of single ropes and often described as being made for “elite climbers.” This is the range that you’ll see most sponsored climbers climbing on, especially for their final send. They choose this rope diameter because it’s lighter (for the approach and the send), and because they do not care as much about durability because they get free ropes. Also, the weight difference of this smaller diameter paired with 70m – 80m rope lengths can be significant.

Seasoned multi-pitch trad and alpine climbers will choose this rope in the pursuit to move light and fast, sacrificing durability. Because this diameter is smaller, there are less sheath fibers, and climbers may notice these ropes don’t last as long.

Ropes in this range can have significantly higher elongation rates. This means when you fall (or even if you take) the rope will stretch and you can find yourself a few moves below, even with a tight top rope. Some leaders like this stretch as it can create a soft catch for a falling leader, even if the belayer is not belaying as dynamically.

These ropes will also run through belay devices quite fast, and some belay devices may not even rated to handle single ropes this small in a single rope configuration. Recently, there have become a number for ropes in this range that are triple-rated as single, half, and twin ropes. This gives them the added advantage of being paired in different ways for alpine, mixed, snow, or ice climbing.

At this diameter, the shorter ropes (~30m) are more often used for glacier travel versus leading indoors.

9.0 MM and below

This area is typically in the realm of specialty ropes for mountaineering, ice, mixed, and alpine climbing. If the rope is a single rope, it’s likely also rated as a twin/half. These skinny ropes prioritize lightweight over durability. This is also why many of them are twin/half ropes — used two at a time to create redundancy.

These ropes often have very high elongation — even on a tight top rope a climber would lose a few moves. These ropes often tend to tangle easily.

Generally speaking, climbers will use these ropes with the understanding that they are fragile. They understand that one sharp rock edge (or accidental crampon kick) could end the ropes life. One notable exception here is Edelrid’s Protect series – the 8.9 mm Swift and the 8.2 mm Starling. These ropes have aramid threads (think kevlar) woven among the standard rope threads to give it significantly more protection over sharp edges.

Rope Diameter Caveat

Rope diameter certifications have a tolerance of +/- 0.3 mm. This means there could be over half a cm of difference between two ropes of the same size. This is the reason that some 9.8’s can feel as thick as a 10.2 and while other 9.8’s can feel particularly skinny.

In the industry, we’ve yet to notice any consistency of one brand running skinny vs one brand running wide.

It’s hard to get more consistent with current rope braiding technology. The manufacturer will pick a diameter, set the machines to create this diameter, and it will be tested by CE/UIAA standards to be within the 0.3 limit on either side.

Summary

Gym ropes are usually between 10.2 – 11mm. When you buy your first rope it will likely be smaller, so take extra care and caution and focus as the belayer. This new rope may feed through the belay device much faster due to its smaller diameter and the fact that it has yet to be used much (no fuzzy sheath or other degradation).

Choosing a rope diameter is often a balance of comfort in the rope handling, along with balancing durability and weight.

9.8 mm – 10.2 mm is an ideal first and second rope. A great rope for top-roping and lead climbing in any ratio.

9.5 mm – 9.8 mm is a common lighter followup, perhaps the third rope buy. It can be a noticeably lighter option for lead climbers looking to own a 70m (or 80m) rope for long outdoor routes.