What is the best way to determine drop handle bar width without having to try out several different handle bars. Is there a shoulder measurement that can be taken?

You could just measure your shoulder width and see what's closest. Personally, I prefer a 42 for the tighter feel even though when measured I've been told I need a 44. The 44 seems too wide, funny how only 2cm can do that.

The other thing to watch for in the bars is the reach - I had to swap from a Ritchey Carbon Logic to a Carbon Streem because the Logic was just too long a reach for me with the 110 mm stem. In the end, I also replaced the 110 with a 100. Yes, I was measured and fit before the bike was ordered - just shows you how personal preference after a few hundred miles goes a long way.

Hold the bars in your hands. The size that feels neutral, without your elbows bending in or out, is best for most people. Some slow-speed tourists like wider bars because it gives them more upper body support when they are sitting up and enjoying the scenery. Some faster riders like narrower bars for better aerodynamics.

The "official" way to measure is the width of the shoulders at the acromium, which is the hard bony corner at the widest point at the corner of the shoulders.

https://www.infovisual.info/03/025_en.html

The other poster's suggestion to hold the bars probably makes more sense if you can do it.

Also remember that various manufacturers measure their bars at different places. The most common difference is whether they measure from center to center of the bars, or from the outside edges. Therefore, one brand's "44" outside-outside would be the same width as another's "42" center to center.

I can't pre-test bars so I had my wife measure my shoulders. 41 cm. My current bars are 42 c-c, so I decided to try 40 c-c bars this time. Frankly, I doubt most of us would notice a size either way, but I read that one source of shoulder /upper back pain (which I occasionally have if I don't concentrate on relaxing) could be too-wide bars, so what the heck.

Im about a 43-44 but I prefer a 42 handlebar.

Many long time cyclists deviate from the shoulder width method. I measure 46 o-t-o and ride with 44 o-t-o. 2 cm really does make quite a difference. 42 o-t-o feels a bit narrow to me.
Good Luck.

Depends on your needs and riding style.

I would normally be riding approx 43 cm c-c bars. I like training on wide bars (went to 44 c-c and 45 o-o for a while) but I am currently using 43 o-o bars. I prefer narrower bars so I can thread tighter gaps in the field. 40 c-c are just a bit too narrow.

In the winter, my square bars are 44 o-o, 43 c-c, so wider. Training on wider bars is nice.

Lemond, not a "shouldery" kind of guy, rode 46 c-c for a while. We all went for that look, emulating him, but it was like trying to steer a motorcycle. That was when I tried the 44s. I went back to 42s for a while, then eventually to 41s.

cdr