Use this calculator to find the minimum theoretical round trip latency between two cities or addresses. You can enter a specific address like: 1600 Pennsylvania Avenue NW, Washington, DC 20500 Or you can enter just a City like: San Diego, CA
You can also enter international addresses by entering the City and the Coutry, for example, Tokyo Japan.
Keep in mind this is the theoretical minimum latency. This assumes a straight line between two points with no equipment to add latency. Depending on the exact physical path the network connection takes, you might see 50% to 300% longer ping times.
For real world examples of ping times, this is a useful tool: https://wondernetwork.com/pings
A fun experiment is to look at the real world times and compare them to the theoretical minimums. You might ask yourself why is there such a large deviance between the theoretical and real world.
To answer that, I recommend looking at some of the maps of undersea and across land cables. You can see some great maps at Smithsonian Magazine and Submarine Cable Map. You will notice that when you check two cities that are near a given line on either of these maps, the theoretical numbers are much closer to the real world numbers.