Is that bug a #16?

Many anglers reference the size of the natural flies they see in terms of a hook size. "Those caddis today were a #16."  That’s a pretty good frame of reference, but it has some challenges.  With all the various brands and styles of hooks available today, a #16 hook has some variability in sizing.  Some patterns produce a bigger bug on a small hook and a small bug on a size or two larger hook.  Confused?

So what really matters to the trout?  The actual size of the natural bug of course.  If you really want to match up your imitation fly to the naturals the fish are eating, put them side by side.  If you want to get geeky about it, measure the real bugs with a micrometer or trace their outline on a piece of paper.  Then you will have a reference for choosing or tying your imitations.

Or you can do what most anglers do and keep trying new flies until something works or you decide to go mow the lawn like you were supposed to.