Below you will see my measurements for an English horn reed. These measurements are approximate and might be longer or shorter by about a millimeter or so, but I think these measurements are a good starting point. Usually, I tie my reeds at about 59mm in total length, then scrape enough cane off to make it look like a reed and scrape the tip thin enough to be able to clip precisely. I’ll clip it down to about 56mm and then start balancing the reed from there, so that it ends up at about 55mm in total length.
These measurements will vary depending on your shaper tip, gouge, and playing preferences. Many English horn players prefer a smaller opening than I do and make their reeds a bit longer. You might also be wondering why I tie on the reed so long if I’m just going to clip off about 3-4 millimeters—that is because if you tie a reed shorter or longer, it will change the shape of the reed. I prefer my reeds to be a bit narrower in width, especially closer to the thread, because this helps keep high notes up to pitch. I could experiment with narrower shaper tips, but my current set up seems to work for me and “if it ain’t broke, don’t fix it!”