Q. What is the latency between Azure regions?

A. There is no official document that outlines latency between regions however you can perform a test to get a rough idea by using some Azure latency/speed test sites from within an Azure VM in a region.

For example create an IaaS VM in a region, such as South Central US. Then within that VM browse to:

Since you are running the site from within a region the numbers found are the latency from that region to the other regions. Below is an example of one latency site running from VM in South Central.