What is the proper way to measure handlebar width for a road bicycle with drop handlebars? But do you measure from the front or the back? Most sources say from acromion process on shoulder to acromion process. I've seen it both ways (here and here). If I measure my wife from the front, she's 38 cm. From the behind-- counting the curvature of her back -- she's 41 cm. Which measurement do I use?

FYI, the acromion process is a $5 word for the bump on your shoulder. See here and here.

I've tried to do my homework but if this has been described elsewhere please let me know and I will RTFM.

Thanks in advance.