How to Tie the Surgeon's Knot

By Alex Clayton · Updated 27 October 2026

The surgeons knot joins two lines by holding them together as one strand and tying a double overhand knot, which is why it is also called the double surgeon’s knot. It copes with lines of different diameter, and experts quoted by MidCurrent rate it easier to tie than the blood knot with cold hands or in poor light.

The trade-off is bulk and strength. Animated Knots notes it is bulkier than a blood knot, and it held less of the line’s strength in one published test (Step 6).

The seven steps below cover choosing it, tying the double and the triple, testing it and the surgeon’s loop.

Step 1: Check the Surgeon’s Knot Is the Right Join

Speed is the surgeon’s knot’s selling point, but it is the wrong join for braid or for two lines of near-identical diameter.

Use it for:

Joining a hooklength to a slightly thicker mainline
Fly leader to tippet, when you want to change tippet size and keep the leader
Adding a dropper, by leaving one tag end long

When the two lines are close in diameter, the blood knot gives a slimmer join. Tom Rosenbauer uses one when diameters are within about 0.001 inch (roughly 0.025mm), while others allow up to two tippet sizes, MidCurrent reports. Braid can slip in a surgeon’s knot, so a double grinner, double uni or FG is usually safer there.

Knot	Best for	Weak spot
Surgeon’s knot	Speed, unequal diameters	Bulky, slight angle, braid can slip
Blood knot	Slim join of similar diameters	Fiddly in cold or poor light
Double grinner, double uni or FG	Braid and bigger diameter gaps	More fiddly to tie

Best for: quick joins between nylon or fluorocarbon of slightly different thickness. Skip if: you need the slimmest join possible or one line is braid.

Step 2: Overlap the Two Lines by Several Inches

Running out of tag end halfway through is the usual reason to start again.

Lay the two lines side by side, pointing in opposite directions.
Overlap them by around 15cm (6 inches) as a guide. Use more if your fingers are cold.
Pinch the overlap between finger and thumb.

The whole length of one line has to pass through the loop on each turn, so feed the short piece (the tippet or hooklength) through and keep the mainline or leader as the long side.

By now you should have two parallel lines pinched together, with the short line ready to work.

Step 3: Form a Loop and Pass Both Ends Through Twice

This is the whole knot. Handle the overlap as a single strand, not two lines.

Form a loop with both lines together.
Pass the tag end of the short line, together with the end of the long line, through the loop.
Pass them through the same loop a second time.

Two passes make it the double surgeon’s knot. In knot terms it is a bend, meaning a knot that joins two lines, and it is structurally different from the binding knot surgeons use, as Knots 3D explains.

Keep the strands lying side by side, not twisted round each other. Crossed strands weaken the knot (see Step 6).

By now you should have a loose double overhand with four ends, two on each side.

Step 4: Wet the Knot, Pull All Four Ends and Trim

A neat surgeon’s knot can still fail if you snug it up dry or pull from two ends only.

Wet the knot with water or saliva.
Pull all four ends slowly and evenly so the turns bed down together.
Finish by pulling the two main lines apart firmly.
Trim both tags close but not flush, leaving a couple of millimetres so the knot cannot creep. Leave one tag long if you want a dropper.

Wetting matters because tightening creates friction heat, which can weaken nylon and fluorocarbon. Pulling only two ends can seat the turns unevenly, so the knot draws up lopsided.

When I change tippet with cold hands on Windermere, this is the join I find quickest to tie neatly.

The verdict: wet it, then pull all four ends evenly and slowly.

Step 5: Add a Third Turn for the Triple Surgeon’s Knot

One extra pass is the standard fix for a double surgeon’s knot that slips.

Repeat Step 3, but pass both ends through the loop a third time before tightening as in Step 4. That gives the triple surgeon’s knot. Four to six turns are possible but add bulk.

Rosenbauer uses the triple when the two materials differ, and Cast and Spear advises three to six turns for braid because it can slip with fewer.

In a Popular Science test, a 4-turn surgeon’s knot joining 30lb braid to 10lb fluorocarbon kept about 80% of line strength. The method was not described, so treat that as a rough guide. If braid still slips, use an alternative from Step 1.

Quick comparison: the double is slimmer and fine for nylon or fluorocarbon joins; the triple grips better on braid or mixed materials but sits bulkier.

Step 6: Test Every Knot and Fix One That Breaks

Some knot sites claim the surgeon’s knot keeps close to 100% of line strength. The same Popular Science test put a 3-turn surgeon’s knot joining 10lb mono to 10lb fluorocarbon at 65%, against 83% for a 5-turn blood knot.

That is one popular-press test with no method described, so treat the numbers as indicative. The tyer matters too: a DuPont representative, quoted by writer Ted Leeson, said the relative strength of the two knots varies a good bit from one person to the next.

Brant Oswald, also quoted by MidCurrent, notes that a double surgeon’s knot can be weak if one strand cuts across the other as it tightens, and advises testing every one before fishing it.

Breaks at the knot: strands crossed, or the knot was tightened dry. Retie.
Slips: too few turns, especially with braid. Go triple or switch knot.
Curly tag or kinked line: friction burn. Retie and wet it first.

Direct recommendation: give each surgeon’s knot a steady, firm pull on both lines by hand before you cast, and retie any that move.

Step 7: Tie a Surgeon’s Loop in the End of One Line

The same double overhand, tied in a single line, gives you a quick fixed loop called the surgeon’s loop.

Double the end of the line back on itself to form a bight.
Tie a double overhand knot with the doubled line.
Wet it, tighten and trim the tag.

Cast and Spear does not recommend the surgeon’s loop as a hook or swivel knot, so use it as a general fixed loop. For alternatives, see our guide to loop knots, or browse the full fishing knots guide for every other join.

Frequently asked questions

Is the surgeon's knot stronger than the blood knot?

Not on the evidence available. One published test put a 3-turn surgeon's knot at 65% of line strength against 83% for a 5-turn blood knot, though the method was not described and results vary with the tyer. Use a blood knot for similar diameters and the surgeon's knot for speed and unequal diameters.

What is the difference between a double and a triple surgeon's knot?

The double passes the ends through the loop twice; the triple passes them through three times. The triple grips better on braid or mixed materials but is bulkier (Step 5).

Can you use a surgeon's knot with braid?

Yes, but only with three to six turns and a firm test before fishing, because braid can slip in a double surgeon's knot. A double uni, FG or double grinner is often the better join. Our fishing knots guide covers the alternatives.

Is the fishing surgeon's knot the same as a surgical knot?

No. It shares the name but not the structure. The fishing version is a bend that joins two lines, whereas the surgical knot binds.