I'm looking to replace my current drop bars. I like the width just fine and would like to get a new set that is the same width (or at least close to it).
How is the width measured? Is it the overall outer width? The width between the center of the bar ends? The width between the inner edges of the bar ends? The width of the flats up until the curve? Something completely different?
The most common measurement I've seen is c-c (centre to centre), the distance between the two horizontal tops of the drops, running parallel with the stem and behind the hoods.
If that doesn't make sense, see the following image.
Image credit bikerumour.com
However, you're right to check this as not everyone does it this way. The internal or external sizes might also be interesting if you're wondering how much space the bike will take to store or what size bar bag might fit between them.
Yes, this answer is a couple years behind. Some manufacturers measure overall outside to outside others center of the tube to center of the tube.(for ease of measuring, center to center is the same as inside edge of one to outside edge of the other) Generally measured at the tips as this provides the easiest point to get an accurate repeatable measurement. The width you choose is based on largely on personal experience but as a general starting point have another person measure the width between the boney protrusions at the outer front of your shoulders(where the clavicle and acromion meet) then add about 2cm for bars measured center to center, or 4cm if they are measured outside to outside. I've heard that for general comfort, having bars slightly too narrow can be more comfortable than too wide because your chest and upper back must do more work to bridge the gap of being too wide. While too narrow could possibly slightly restrict maximum breathing capacity and also cause elbow-knee interference. However issues with being too wide or narrow also depend on other factors like reach, bar/drop height, leg length ratio, etc.
Overall I think folks make all the wrong fuss over these sort of measurements, the optimums are rarely steep peaks on a graph, most often the optimum is just the middle of a nice wide gentle curve with plenty of margin for error.(ie cranks for the xs to xl frame range should span about 150 to 185[~25% or people 5'>6'4"] based on femur lengths and knee bending, but good luck finding anything outside of 170-175[~3%]. Meanwhile people will worry for days over 170 vs 172.5[~1%]) I mean my motorcycle has 80cm handle bars and my mountain bike 58cm my old roadbike 40.5cm, half that of my motorcycle.(I did find this a little bit cramped for my body but it never caused any notable issues) and other than the shock of transitioning between them if it has been a few months, they all work well enough.
An increasing number of handlebars have the drops flared outward. This trend started with gravel bikes, but it is starting to make its way to road bikes - in 2013, it would have been considered very strange on road bikes.
As far as I can tell, just about everyone is now reporting width center to center, and most bars are measured at the hoods. However, the drops on flared bars are wider than the hoods. Take note that all else equal, a narrower handlebar width decreases your reach to the handlebar.
The handlebars on the 2024 Trek Madone handlebars have width measured at the drops. The ones on the 2024 Wilier Verticale are measured at the hoods. So, do pay some attention to where the width is measured. I remember that width tended to be measured at the hoods on pre-2024 bars.
Some handlebars will report the width both at the drops and at the hoods in the detailed specs chart. For example, the ENVE SES AR handlebar's smallest size is 38.5cm at the hoods, 43.2cm at the drops. Of course, the bar's nominal width is listed as 38cm. Gravel bars tend to flare more. Road bars have tended not to have any flare prior to 2024. The AR in the ENVE bar stands for all-road, which encompass paved and unpaved roads, and it was released in maybe 2021 or so. Additionally, the 2024 handlebars/integrated cockpits on some aero bikes have a slight flare.
If a manufacturer doesn't report the width at the drops or the amount in cm by which the drops are flared, but it does report how many degrees the drops are flared outward (distinct from outsweep, as explained later), you can use trigonometry to calculate the additional width in the drops.
Let ⍺ be the flare angle. For example, the Zipp SL 80 Race handlebar reports a 5 degree flare angle. Assume all the arrows go center to center; the graphics are due to the limitations of Google Sheets. The handlebar drop is described as 125mm, which is a very standard parameter that's always reported these days. Let d be the additional distance each drop is away from the centerline of each hood (i.e. the total width at the drops is the reported width + 2d).
d = drop * tan(⍺)
If using Google's search bar calculator, make sure you select the degrees mode (as opposed to radians). Entering the 5 degree drop angle and 125mm drop, I get 10.93mm, so the total width at the drops for a 38cm bar is 40.2cm. This is a pretty small amount of flare, and I think most bars with flare have more of it at the time I wrote this.
Bars that have outsweep angle the drops relative to the hoods. A bar with flare but not outsweep will have the drops parallel to the handlebar at the hoods. The Zipp bar reports 8 degrees outsweep. Most road bars don't have it, and gravel bars with outsweep will tend to have more than 8 degrees.
On some swept bars, the section of the bar where the hoods mount is vertical (the ENVE SES AR being one of these, if memory serves right). On others, that section of the bar is angled, which means your hoods are also angled. This may or may not be what you want. Keep in mind that in modern levers, companies are starting to angle the levers out a bit. This feature is not typically explicitly stated, and there is no short name for it. You have to infer by the photo. And unfortunately, the Enve SES AR's photo doesn't show clearly, even though one of the comments clearly alludes to it. Perhaps it's not a material difference with the Zipp bar above, but it can be a material difference on gravel bars with a lot of flare. If they had asked me how to label this, I'd have said hoods mounted straight or angled. But they didn't ask me.