Model railroading scales are used to ensure that when you place one freight car next to another that it looks correct and they fit on the same set of railroad tracks. Some of these model train scales are recognized globally, some less widespread, and some are only in the small circle of hobbyists that decide to create their own model trains.
A few of the more recognized model railroading scales include the following:
The ratio measured for each of these model train scales refers to the distance between the tracks. There are some tracks that have dual gauges and are able to hold two different model train scales at the same time.
The best size of model train for you or your interested loved one has to do with your interests. Larger scale models often have more detail in accordance to the actual train. There is more space to add intricate details; however, smaller scales are getting more and more detail and are great for not only collecting model trains, but creating the ambiance for them as well. With smaller scales you can make intricate tracks through tunnels around mountains and more. Use things like amount of space available, and uses for your model trains to decide which model railroad scale is best for you.