What is the strongest knot?

Every Pathfinder has heard of a strongest knot in the world. The labs tell a different story: every knot takes away part of a rope's strength, and the knot that does best in one test can slip or jam in another situation. This guide gathers the tests published by CMC Rescue, a US rescue equipment company, explains why the numbers vary and shows where 15 knots from the catalog fail. At the end, you will learn how to check a knot and how to compare knots with string, with nobody hanging from anything.

🏆What is the strongest knot in the world?

It does not exist. People looking for the strongest knot usually want two things: for the rope to hold as much load as possible with the knot in it, and for the knot never to come undone by itself. Those are different qualities, and the same knot can do well at one and poorly at the other.

On strength, no knot in the tests kept 100% of the rope's strength. Inside a knot, the rope makes tight bends over itself, and instructors at the CMC Rescue school summed up the rule in 2023: bigger diameter, bigger bends, higher efficiency. In the 2014 tests, the rope broke most of the time at the first bend, where it enters or leaves the knot.

The tensionless hitch is often named as the exception: the rope wraps several times around a tree trunk, and friction holds the load before it reaches the end. Rigging Lab Academy, a platform for rope rescue courses, speaks of efficiency close to 100% without publishing the test behind the figure. The Animated Knots guide, an international reference on knots, records that reputation, adds that the advantage is more theoretical than practical and calls for a trunk at least eight times the rope's diameter.

On security, a Massachusetts Institute of Technology (MIT) study published in the journal Science in 2020 used fibers that change color under pressure: knots with more crossings and more neighboring segments twisting in opposite directions hold better. That math explains why the reef knot beats the granny knot, which looks almost identical, and why the Zeppelin bend did better than the alpine butterfly, another common climbing knot.

📊How much does a knot weaken a rope?

The most quoted numbers in technical rescue come from CMC Rescue. In 1987, the company tested 18 knots in rope and 8 in webbing for the first edition of its rescue manual, the CMC Rope Rescue Manual. In 2008 and 2014, it repeated part of the tests on 12.5 mm rope, first nylon and then polyester, with at least five samples per knot. John McKently, director of the company's school, presented the comparison at the 2014 International Technical Rescue Symposium (ITRS).

Efficiency is the share of strength that remains: if the rope without a knot breaks at 100 units of force and with the knot breaks at 75, the efficiency is 75%. In Brazil, the height rescue course handbook of the Espírito Santo Military Fire Department (CBMES, 2026) gives numbers of the same order, such as a 45% loss for the clove hitch, which the catalog teaches tied with the rope end. The similarity has a likely explanation: the handbook says it took the percentages from the manuals in its bibliography, and one of them is Confined Space and Structural Rope Rescue, one of the books that, according to McKently, reproduced the 1987 tests.

Efficiency in 12.5 mm rescue rope, with at least five samples per knot in 2008 and 2014. In the figure-eight loop, the load goes on the loop; pulled end to end, with no load on the loop, it held 74% (2008) and 54% (2014). Source: John McKently, CMC Rescue (ITRS 2014).

🔬Why do knot strength numbers vary so much?

The knot is only part of the story. Material counts: McKently's team wondered whether polyester, which is slicker, would make knots more efficient, but the 2014 series came out lower than the 2008 series for six of the eight knots, and the bowline dropped from 75% to 58%. Water also moves the numbers, with no clear pattern: after an hour underwater, the nylon rope gave 67% with the bowline, against 75% dry, and more than dry with the figure-eight loop.

Diameter matters even more. In 2023, LeRoy Harbach and McKently presented the results of 487 tests: averaged over seven knot configurations, ropes with a polyester sheath kept 54% (9.5 mm), 60% (11 mm, traditional construction) and 65% (12.5 mm). The authors admit that 15 years of data, from different machines and people, are incomplete and probably inconsistent, and they recommend that rescue teams use 50% in safety calculations until new tests show otherwise.

In fishing, the yardstick is different. According to Animated Knots, monofilament line with a knot in it breaks at around half of its ideal strength, so promises of 100% deserve suspicion. The Palomar knot appears in the same guide among the strongest and most reliable fishing knots; choosing one for each hook is covered in the guide to the best knot for a fishing hook.

These tests provide an estimate of what you can expect.John McKently, director of the CMC Rescue School, ITRS 2014

⚖️What is the most secure knot, and why does the reef knot fool people?

The reef knot (square knot) shows that strength and security are separate things. The CBMES handbook lists a loss of only 15% to 20% for it, a strong knot's number, and still includes it only with a backup knot. It capsizes: pull one of the ends outward, and the knot changes shape and slips. Animated Knots says never to use it for a critical load; see the guide to the knot to join two ropes.

The most common mistake starts with the half knot, each half of the reef knot. When the second half knot repeats the direction of the first, you get the granny knot, which Brazilian manuals call nó torto or nó esquerdo. Under heavy load it can slip and, once tight, it can jam.

The bowline holds well under load, but without load it can come loose easily, according to Animated Knots, and the CBMES handbook also calls for a backup on it. The water bowline adds an extra half hitch, which forms a clove hitch and holds the tail better.

The clove hitch starts lashings, but it slips and, backed up with too many half hitches, it can jam after a heavy pull. The round turn and two half hitches ties a load to a post or ring: the round turn takes the first strain while you finish the half hitches. The sheepshank, which shortens a rope, is the extreme case: Animated Knots shows a well-tied sheepshank in synthetic rope failing under a modest load.

🔒Which knot won't come undone, and when is that a problem?

The double fisherman's knot is the picture of a knot that won't let go: it was the most consistent in the CMC tests, close to 80%, and Animated Knots recommends it for joining climbing ropes and closing a prusik loop. The price comes after loading: it can jam so hard that it never comes untied.

The Zeppelin bend is the counterexample: secure under load, with little tendency to slip or jam, and it unties after a heavy load, never while it is still loaded. Animated Knots presents it as an alternative to the double fisherman's precisely because it does not jam, as long as the tails are left long.

At the end of a rope, the figure-eight knot unties easily even after being pulled tight against a pulley, but it can fall out. When the end has to stay firmly in place, use the double overhand stopper, bigger and more stable, which also works as a backup for other knots.

With the figure-eight follow-through loop, the care is in the pattern: retraced along the same path, it gives the same figure-eight loop as in the table, and the strands must lie in pairs, side by side. The CBMES prefers the figure eight precisely because the team can easily see whether it is tied right. We found no reliable published test showing how much more strength a figure eight with crossed strands loses; Animated Knots only says that, well dressed, it handles load better. Always dress it.

📋What are the strongest types of knots, and where does each one fail?

The table lists the 15 knots in this guide with the difficulty rating from the catalog, where each one has a video and step-by-step instructions. Knowing where each one fails is a requirement: the Knots and Lashings Honor (AR-040) asks you to tie at least 20 knots from memory and explain the use and limitations of each, as the guide to the Knots and Lashings Honor requirements shows.

Difficulty: Desbravai catalog, checked on Oct 6, 2026.

✅How do you know a knot is tied correctly?

Before you trust a knot with weight, run four checks. Dress it: the strands run smooth, with no twists, in the pattern shown in the catalog. Set it: pull each strand that enters and leaves the knot, one at a time, until everything sits snug; Gravitec Systems, a US fall protection company, calls these two steps dress and set.

Check the tail: the end must be long, to the standard explained in the guide to rescue knots, and a stopper knot helps keep it in place. Ask for a check: someone else looks at the knot before it takes weight, and the instructor always checks it when the knot will hold a person; for climbing, the routine is in the guide to climbing knots.

🧪How can you test knot strength without putting anyone at risk?

A Unit meeting, led by the Counselor, is enough to see what the labs measure. You need thin cotton string, two broomsticks, two sturdy tables, a bucket with a handle, a one-liter jug and safety glasses, because a string that snaps under tension can whip back.

Rest one broomstick across the two tables. For the no-knot sample, wrap the string four or five times around it and as many times around the second broomstick, which holds the bucket, and tape the ends down: these are miniature tensionless hitches, and friction spares the ends. Then make identical samples with a knot in the middle: a figure-eight knot, or two ends joined with a reef knot or a double fisherman's.

Pour in one liter at a time (about 1 kg) and write down how many liters each sample took before it gave way, and where. Make at least three samples of each type, because a single test is misleading. Expect the knotted string to give way first, near the bend where it enters the knot. If the reef knot slips before it breaks, note it: that is a security failure.

The rules do not change: the bucket hangs a hand span above the floor, nobody puts a foot or hand underneath or stands facing the string, the test uses only string, and no knot is ever tested by hanging a person from it. Real rope, with people on it, is for the instructor and certified equipment; to keep the club's rope in good shape, see how to care for rope.