|Measure the distance between the bony protrusions in your shoulder joints, this will give you a rough idea of the bicycle handlebar size you require. Then add a further 2cm to your shoulder measurements to allow for the natural radiating of your arms when riding.This guide is for road bike and cyclocross handlebars which are measured from center to center. Each manufacturer measures their bars differently! Make sure you check whether the bars you are looking at are measured center to center or outside to outside. if your bars are measured outside to outside you need to add a further 4cm to your arm measurements to account for this difference.
This guide will give you a rough idea of the handlebar width you require. However, it is important that you are comfortable! Riders choose different widths depending on their riding style. It is also important to consider when choosing a handlebar, a wider bar opens the chest for better breathing and greater leverage, whereas a narrower bar is more aerodynamic. With Track Bikes you would usually go down a bar size. With Cyclocross bikes, riders often go up a size.
Since each bar is offered in two different Reach/drop dimensions, you will also need to choose those options. The medium R/D is 80/135 and the large is 90/145. This is greatly determined by personal preference. If you feel like you need to be more stretched out, go with the large R/D. If you feel like you are too stretched out, go with the medium R/D. Cyclocross handlebars are usually best as compact, so you would want to choose the Medium R/D for cyclocross riding.