The ones I got from Jean were 35" long. They are very "beefy", but were of the fully doubled format shown in the above photo ... and admittedly a bit too short for effective use (by someone my size, anyway - i.e. 6' 4".)
However, I solved that problem easily enough by severing
one of the cords flush with the top of the fixed turkshead knot (i.e. the knot that doesn't slide) which forms the short standing loop at the end you attach to the lanyard swivel. I then carefully pulled the severed end back into the
sliding turkshead knot and sewed it firmly in place . (By actual experience

I learned that you must be careful not to pull that severed end of the cord
through the knot, because it can be difficult ... though not impossible ... to get it fed back into the knot. While sewing it into the knot, you must also avoid catching the other cord with the thread, of course, so that knot will remain a "slider".) That procedure resulted in very stout and
long lanyards of the more functional kind - i.e. with the smallish fixed loop on one end, and adjustable loop ("noose") on the other.
I also have several lanyards that were originally of that "single strand" variety (though made of somewhat thinner cord - still plenty sturdy, mind you) but darned if I can remember where I got them ....

Will try to figure that out, and post the source ....
I
don't like lanyards that have a metal clip for attaching to the pistol - noisy and likely to damage the pistol finish, as far as I am concerned. The traditional British method of attaching lanyards (though it does require a decent size lanyard ring) is to pass the end of the short (fixed) loop through the swivel ring, then pass the rest of the lanyard back through that loop and draw it tight ... very easy on the pistol finish, and impossible for it to come loose unless the lanyard itself breaks .... like this -
(By the way, as you can probably tell by the butt configuration, that is a Colt New Service in the lower photo .... the upper one is an 1884-dated - and thus unregistered "antique" - .476 MkII Enfield revolver, NWMP issue ....)