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If I'm climbing down a rope, and get near the bottom, how much would I have to be carrying to break the rope?

What is the strength of a standard 50 foot rope from the equipment list?

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  • \$\begingroup\$ @EricLippert I don't think there's any hidden sophistication behind the question — if there was, such model details would be the subject of the question, and it wouldn't include a common misconception without commentary. If you want to correct the common misconception and can figure out how to incorporate that side discussion into an answer that's otherwise on-subject of the question's main thrust, that's the best place for such material. \$\endgroup\$ – SevenSidedDie Nov 15 '17 at 20:24
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So, given @Szega's very, very valid "5E is not a physic simulator" point but running with the suggestion of extrapolating from the DC 17 strength check anyway...

The 5E lifting and carrying rule is quite coarse:

You can push, drag, or lift a weight in pounds up to twice your carrying capacity (or 30 times your Strength score).

If we assume that a +7 to Strength will hit a DC 17 reliably, that means 24 Strength (only monsters can break ropes every time, it seems) ... and 30 × 17 gives 720 lbs.

The answer from @chaoticgeek looks at real-world ropes and gives 675lbs as the "safe load factor" — ¹⁄₁₂th the tensile strength. The number based on the DC is right in that ballpark, and if we use 12× ~700lbs as maximum load with stress, we get around 8500 lbs. So this all seems reasonable.

Or, one could argue that someone with Str 4 — a -3 bonus — can hit a DC 17 some of the time, and that the safe load should cover that, because that's what "safe" means. That gives a safe load for standard hemp or silk rope at only 68 pounds, with max weight at a little over 800 lbs. This one seems low.


Also, note that the uncommon magical item Rope of Climbing says:

This 60-foot length of silk rope weighs 3 pounds and can hold up to 3,000 pounds

But it doesn't have a given strength DC to break. Instead, it has AC 20, 20 hit points, and (slow) regeneration. So it's probably safe to just say that its limit doesn't necessarily correspond to that of regular rope.

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    \$\begingroup\$ I don't think you can compare load to DC like that. A result of 17 represents an average, repeatable effort by somebody with a +7 strength bonus, or STR 24 (yes, yes, above human maximum; that just means no human can reliably break a rope by main force). That yields a maximum drag capacity of 720 lbs, which using your load factor calculation, would give it a breaking load of over 8600 lbs. \$\endgroup\$ – Darth Pseudonym Nov 15 '17 at 15:35
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    \$\begingroup\$ @DarthPseudonym That's probably better. I'll adjust. \$\endgroup\$ – mattdm Nov 15 '17 at 15:39
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    \$\begingroup\$ Interestingly, that puts the load and breaking strength right in the same realm as Chaoticgeek's calculation based on a real 1" hempen rope -- about 11% difference. \$\endgroup\$ – Darth Pseudonym Nov 15 '17 at 15:47
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    \$\begingroup\$ Since magic items tend to be SIGNIFICANTLY harder, if not downright impossible to break, it stands to reason that magic rope would have such a vastly different limit. \$\endgroup\$ – ThunderGuppy Nov 16 '17 at 21:18
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However much your DM says.

DnD 5e is not a physics simulator and does not bother with that level of detail. The only guidance the PHB offers is that "it can be burst with a DC 17 Strength check" (p.153). If you are so inclined you could try to convert that DC to a weight limit, but the system is not built like that.

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    \$\begingroup\$ According to the chart posted by @chaoticgeek I would have to raise that DC myself, I find it hard to believe that a DC 17 is sufficient to produce ~7,000 pounds of force. But it is a game after all. \$\endgroup\$ – Slagmoth Nov 15 '17 at 13:59
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    \$\begingroup\$ That chart is based on rope made from materials found on earth. D&D rope is based on materials found in popular fiction, which have a well documented history of having a tensile strength inversely proportional to the dramatic tension of the scene. \$\endgroup\$ – Derek Stucki Nov 15 '17 at 15:01
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    \$\begingroup\$ @Slagmoth, a DC 17 check wouldn't produce 7000 pounds of sustained force, but a hard, fast pull could produce a brief spike that high. \$\endgroup\$ – Mark Nov 16 '17 at 1:49
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    \$\begingroup\$ While it's not a physics simulator there pay attention to weight in terms of carrying capacity, so they should pay attention to what happens to said character on a rope because that's one of the main uses of a rope. (I climb down the rope. I lower the horse down with the rope. I lower the elephant down with the rope.) \$\endgroup\$ – Loren Pechtel Nov 16 '17 at 4:48
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    \$\begingroup\$ @Slagmoth Also pounds force is different from total weight. I haven't looked at chaoticgeek's chart, but something having a weight limit of 31kN is way different from a max impact force of 31kN. Typically the max impact force of a rope is substantially lower than the total load it can bear before snapping. A modern climbing rope for example can lift a school bus but can only handle 10kN or so max impact force. \$\endgroup\$ – TylerH Nov 17 '17 at 6:14
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This page shows various pound (force), expressed as lbf, for a hemp rope of given diameter to break. If we assume that hemp rope in D&D is constructed in similar ways then according to the chart a 1" diameter rope has a minimum breaking strength of 8100lbf, and a safe load factor (1/12 the breaking strength) of 675lbf. And through some searches 1lbf = 1lb of weight.

So in general your 1" rope could stand up to 8100lbs before it would snap, and safely 675lbs to not stress beyond a safe load. The safe load would take into account any sort of large movements, swinging or falling and grabbing the rope, that could cause more force beyond the weight on it or general wear and tear.

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    \$\begingroup\$ According to that chart the rope in the PHB would be 7/8 (or 13/16) in diameter based on the weight described as a 1" diameter rope 50' long would be ~13lbs. If you really want to split hairs. \$\endgroup\$ – Slagmoth Nov 15 '17 at 13:57
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    \$\begingroup\$ Yeah, I just picked 1" because I thought it said that in the PHB. I think that may have been 3/3.5 that it said it was 1" thick. \$\endgroup\$ – chaoticgeek Nov 15 '17 at 14:50
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    \$\begingroup\$ I imagine poor knotting can also promote failure, whether of the knot or the rope itself. \$\endgroup\$ – Danikov Nov 16 '17 at 11:51
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    \$\begingroup\$ Yeah, if you wanted to add more checks with knotting you would probably want to make sleight of hand checks for knotting the ropes. \$\endgroup\$ – chaoticgeek Nov 16 '17 at 15:13
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    \$\begingroup\$ I would think "profession sailor", or "survival" more apropriate checks. \$\endgroup\$ – Jasen Nov 20 '17 at 1:40
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Just use common sense: assuming you are playing in a kind of medieval technology world like Forgotten Realms, and this is not a special rope made of some rare material, hemp rope of about 8–12mm should do, which would yield a breaking strength of from 900 to 2385 pounds. The length of the rope actually has nothing to do with it (other than it adds to the weight)

Remember most climbing ropes break at the knot or at some edge. So depending an care and knowledge, it could break significantly sooner.

I also found a 1E reference that gives 1500 lbs as a figure, which fits with the real-world range above.

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    \$\begingroup\$ "Length of the rope has nothing to do with it...." Imperfections in ropes occur with some frequency; as a rope grows longer--or rather, as the section of a rope being loaded grows longer--the break-strain of the weakest included point goes down. (Something like root-length, but it's been decades since my last mechanics class.) \$\endgroup\$ – nitsua60 Nov 15 '17 at 14:24
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    \$\begingroup\$ One could assume that a properly manufactured rope has been load-tested and bears the given weight as minimum. The imperfections would then only determines where it brakes when it actually exceedet load. But I think that is more a topic for Physics, rather than role-playing. We could also talk about dynamic load etc. \$\endgroup\$ – Daniel Nov 15 '17 at 14:33
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    \$\begingroup\$ The longer the type the more likely it is to snap, this come from personal experience around hemp rope \$\endgroup\$ – Garret Gang Nov 15 '17 at 15:13
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The best real-world equivalent is Manila (Jute) rope. It supplanted the use of hemp rope in ship rigging, and is the strongest natural-fiber rope easily available. It's much more durable than cotton or hemp, stronger, more flexible, resists salt water damage, weathers well, and gets more "tooth" (friction) over time and use, making knots grip stronger. It also floats on water.

Rope strength depends on thickness and material. A 50ft spool that weights ten pounds corresponds to a thickness of one inch. The break strength on a one-inch Manila rope is 8,100 lbs. Cotton weighs slightly less, but it's break strength at that weight/50ft is only 3,000 lbs.

I actually couldn't find the tensile strength of silk rope, because it's now most often used for... private things.

Manila Rope @ engineeringtoolbox.com

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As Szega says there are no specific rules for this but the characters are assumed to be competent and climbers are never caught without a sufficiently strong rope so the same should hold true for adventurers.

I would have this as a non-issue personally.

If you as a GM want the rope to snap consider it rubbing on a sharp piece of rock rather than a weight check.

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    \$\begingroup\$ In story circumstances can complicate this... Multiple characters using multiple ropes tied together, one character carrying another, plate-mail plus gear can be heavy, especially for larger humanoids like half-orcs. \$\endgroup\$ – Aviose Nov 15 '17 at 16:33

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